If you are deciding between Kenmore 200 series model 81214, 400 series model 81414, 600 series model 81614, BC4026 & BC4027, Kenmore Elite 21814 & 81714 bagged canister vacuum cleaners, the comparison information here may be helpful to you.

images from kenmore.com & kenmorefloorcare.com

Some popular specific comparisons:

• 200 series vs 400 series vs 600 series
  (81214 vs 81414 vs 81614)
  The difference between Kenmore 200 series 81214, 400 series 81414 and 600 series 81614 is:

  200 series model 81214 uses paper bags (not HEPA bag) while the 400 series model 81414 and 600 series model 81614 use HEPA cloth bags.
  (All of them have HEPA filter.)

  The 200 series model 81214 has the On/Off control on the canister, while the 400 series model 81414 and 600 series model 81614 have it on the handle. Fingertip control allows you to turn on/off the vacuum and turn on/off the brush roller without bending over.

  The 400 series model 81414 and 600 series model 81614 have a Check Bag Indicator whereas the 200 series model 81214 does not have. The Check Bag Indicator light comes on whenever the airflow becomes blocked.

  The 200 series model 81214 is Orange, the 400 series model 81414 is Red and 600 series model 81614 is purple.

  The 200 series model 81214 has a standard wand whereas the 400 series model and 600 series model 81614 have a telescopic wand.

  The 200 series model 81214 and the 400 series model 81414 comes with 3 attachments: a Crevice Tool, a Dust/Upholstery Brush, and a Bare Floor Tool; while 600 series model 81614 comes with 4 attachments: a Crevice Tool, a Pet PowerMate, a Dusting Brush, and a Bare Floor Tool.

  The 200 series model 81214 has a 24-foot power cord, the 400 series model 81414 cord length is 26-foot and 600 series model 81614 has a 28-foot cable.

• Kenmore BC4026 vs BC4027 vs 81614
  All of them belong to 600 series.
  The main difference between Kenmore 81614, BC4026 and BC4027 Pet-Friendly bagged canister vacuum cleaners is the included PowerMate motorized floor nozzle.
  The BC4027 has Ultra Plush System – the PowerMate nozzle has vent inlets allow it not to be sealed down on high pile carpets, according to Kenmore, this makes the Ultra Plush nozzle up to 32 percent easier to push-pull on thick carpeting for smooth maneuverability.
  And the BC4027 has a headlight on the nozzle to help illuminate low light spots for a thorough cleaning.
  While the PowerMate nozzle on the BC4026 and 81614 does not have these features.

  Cleaning Reach
  According to specifications on kenmorefloorcare.com product page, the BC4026 has a 9.5-foot telescoping wand versus 10.5-foot on the BC4027 and 81614.

  Color
  The BC4026 is blue, the BC4027 is red whereas the 81614 is purple.

Difference between Kenmore 81614 vs 81615
According to the customer support, the 81615 is a newer model with a different exhaust filter. The 81614 and 81615 perform identically.

• Kenmore 81614/81615 vs 81714

  The designs of the canister of 81614/81615 and 81714 are a little different.

  The Elite 81714 has Ultra Plush System PowerMate nozzle for smooth maneuverability on thick carpets while the 81614/81615 nozzle does not feature the Ultra Plush System.

  The Elite 81714 has a headlight on the nozzle and a light on the wand whereas the 81614/81615 has no lights.

  The 81614/81615 has a 28-foot cord versus 26-foot on the 81714.

  The 81714 is Champagne/Gray while the 81614/81615 is Purple.

  The 81614/81615 has a Pop-N-Go floor nozzle whereas the one on the 81714 is not.

  The 81714 weighs 22 lbs while the 81614/81615 weighs 22.6 lbs.

  The 81714 attachment reach is 10-foot versus 10.5-foot on the 81614/81615.

• Kenmore BC4027 vs 81714
  The designs of the canister are a little different.

  The Elite 81714 has a headlight on the nozzle and a light on the wand whereas the BC4027 has only the headlight.

  The 81714 is Champagne/Gray while the BC4027 is Red.

  The BC4027 has a Pop-N-Go floor nozzle whereas the one on the 81714 is not. Not a big deal.

  The 81714 weighs 22 lbs while the BC4027 weighs 24 lbs.

  The 81714 attachment reach is 10-foot versus 10.5-foot on the BC4027.

• Kenmore Elite 81714 vs 21814
  The key difference between Kenmore Elite 81714 and 21814 is the floor nozzle. The 81714 has an Ultra Plush nozzle while the 21814 has a CrossOver nozzle – the bare floor nozzle is connected and nested inside the motorized nozzle.

  Both have 2 motors, however, the 21814 has a inducer motor which is more powerful than the conventional Kenmore upright vacuum motor. Whereas the 81714 does not have a inducer motor.

  The 21814 nozzle has dirt sensor to help you find hidden dirt you cannot see whereas the 81714 nozzle has no dirt sensors.

  The 21814 has a light on the wand whereas the 81714 has a headlight on the nozzle and a wand light.

  The attachment reach of 21814 is 11-foot versus 10-foot on the 81714.

  The 21814 comes with a Pet PowerMate, a Dusting Brush, a Floor Brush, a Crevice Tool, and a Fan Tool whereas the 81714 comes with a Pet Powermate, a Dusting Brush, a Floor Brush, and a Crevice Tool.

  The 21814 weighs 23 lbs versus 22 lbs on the 81714.

  The 21814 is silver whereas the 81714 is Champagne.

Difference between Kenmore BC7005 vs 21814 vs 81615/81614
The BC7005 and 21814 are almost the same apart from the color. The Kenmore BC7005 is Rose Gold whereas the 21814 is Silver.
The 81615/81614 has a Pop-N-Go floor brush whereas the 21814/BC7005 have the bare floor tool nested in the power nozzle which can be lifted away from the power nozzle for hard floor cleaning.
The Pop-N-Go floor brush is an accessory that stores inside of the canister body and can be attached to the wand in a snap.
The 21814/BC7005 have Electronic Dirt Sensor that helps you clean more thoroughly whereas the 81614/81615 does not have the Dirt Sensor.
The 21814/BC7005 have a wand light to illuminate dark spots whereas the 81615 doesn’t.
The 81615/81614 comes with a Crevice Tool, Pet PowerMate, Dusting Brush, and Bare Floor Tool.
The 21814/BC7005 comes with a Pet PowerMate, Dusting Brush, Floor Brush, Crevice Tool, and a Fan Tool.

Difference between Kenmore BC3005 vs 81414
The Kenmore 81414 is Red whereas the BC3005 is Blue.
The hose end that connects to the canister is a bit different. The one on 81414 is straight whereas the one on BC3005 is angled.
The BC3005 has a brushroll status indicator light and automatic brushroll reset function, whereas the 81414 has manual overload protector reset button which has no light.
The BC3005 also includes a bonus 2-pack of bags.

Difference between Kenmore BC2005 vs BC3005
The Kenmore BC3005 is Blue, it comes with a Motorized floor nozzle, a Crevice Tool, a Dust/Upholstery Brush, and a Bare Floor Tool.
The BC2005 is Green, it comes with a suction only floor nozzle which does not have a motorized brush, a 3-in-1 Combination Tool, and a Bare Floor Tool.

Difference between Kenmore BC7005 vs BC3005
The Kenmore BC7005 features an Inducer Motor which is more powerful, the suction power on the hose end is over 280W whereas the BC3005 is 210W.
The BC7005 has a lift away floor brush integrated into the power nozzle.
The BC7005 equipped with a wand light and dirt sensor whereas the BC3005 does not have these.
The cleaning reach of BC7005 is 11-foot versus 9.5-foot on the BC3005.
The BC7005 has “stair grip located on lower body of the canister will aid in preventing the canister from slipping when used on stairs”, whereas the BC3005 does not have.
The BC3005 comes with a Crevice Tool, Dust/Upholstery Brush, and Bare Floor Tool. Besides these tools, the BC7005 also comes with a Pet PowerMate and a Fan Tool.
The Kenmore BC7005 is Rose Gold whereas the BC3005 is Blue.

For general comparison of these Kenmore bagged canister vacuum, you can read the comparison table below:

Similarities:

• Have Automatic Cord Rewind allows you to push a button to retract the cord with no need to winding by hand.
• HEPA Filtration System trap 99.97% of debris, dust, pollen and other particles down to 0.3 microns inside the vacuum, reduce the pollutants in your room, so you breathe cleaner air.
• Height Adjustment
  There is a height adjustment pedal on the rear of the
  PowerMate nozzle, it has 4 height adjustment settings to fit different surface cleaning needs.
  HI setting for Shag, deep pile, super-soft, or ultraplush carpets, and scatter rugs.
  MED setting for Medium to deep pile.
  LO setting for Low to medium pile.
  XLO setting for other carpets and bare floors.
• Suction Control on the handle allows you to adjust the suction power to clean different surfaces.
• Fingertip Control allows you to turn on/off the brush roller without bending over.
• Have Edge Cleaners are on both sides of the PowerMate to help clean along base-boards or remove dirt trapped at carpet edges.
• Have places to store the attachments.
• Carry one year limited warranty.

The Pet PowerMate is designed for removing pet hair from furniture, carpet, stairs and more;
the Dusting Brush is for dusting furniture, drapes, walls, etc.;
the Crevice Tool can be used to clean between cushions and other nooks and crannies.

Download manuals to learn more:
Kenmore 200 series model 81214 manual:
https://i.sears.com/s/d/pdf/mp-tc/10128154/prod_19266688012

Kenmore 400 series model 81414 owner manual:
https://i.sears.com/s/d/pdf/mp-tc/10128154/prod_19266687912

Kenmore 600 series 81614 user guide:
https://i.sears.com/s/d/pdf/mp-tc/10128154/prod_2319157912

BC4026 user manual:
http://kenmorefloorcare.com/product_images/manuals/BC4026%20Manual%20GB%20V4_20200508.pdf

BC4027 manual:
http://kenmorefloorcare.com/product_images/manuals/BC4027%20Manual%20GB_ES%20V2_20200429.pdf

Kenmore Elite
21814 manual pdf:
https://i.sears.com/s/d/pdf/mp-tc/10119637/prod_19263324112

81714 manual:
https://i.sears.com/s/d/pdf/mp-tc/10119637/prod_19263316312