In this post, DC15 refers to DC15 Animal, DC25 refers to DC25 Animal.
Dyson DC15 VS DC25 Comparison
images from manufacturer

Compared to DC15, the big cons of DC25: smaller dirt container and shorter cord. But the DC25 is lighter.

Bin Capacity
DC15 has a much larger bin.
The bin capacity of DC15 is 0.71 gallons while DC25 has a 0.31 gallon bin.

Cord Length
DC15 have a much longer cord.
The cord length of DC15 is 37 ft cord whereas DC25 has a 24.6 ft cord.

Motor Rating
DC15 has a 10 amp motor while DC25 has a 11 amp motor.

Size
The dimensions of DC15 are 44.09″ x 13.66″ x 11.41″ while the dimensions of DC25 are 42.4 x 12.2 x 15.4 (HxWxD).

Weight
DC25 is lighter.
DC15 weighs 19.95 lbs while DC25 weighs only 16.12 lbs.

Tools
DC15 comes with a carpet care kit, mini turbine head and low-reach floor tool; whereas DC25 comes with a combination accessory tool, mini turbine head, and stair tool.

Price
DC15 is cheaper.
At some online stores, DC15 costs less than $400 while DC25 costs about $500 when this article posted.

Both of the vacuum cleaners are bagless and have suction power of 220 airwatts; they feature Dyson’s Ball technology, Root Cyclone technology; come with motorized brushbar, lifetime washable HEPA filters, telescope reach wand, and carry 5 years warranty.

DC17 or DC24 which is better? Read the comparison below.
In this post, DC17 refers to DC17 Animal, DC24 refers to DC24 Animal.
Dyson DC17 vs DC24
images from manufacturer

Suction Power
DC17 has much more suction power.
DC17 has a suction power of 220 air watts while DC24 has only 115 air watts.

Motor Rating
DC17 has a 12 amp motor while DC24 has a 6.5 amp motor.

Movement Type
DC17 uses fixed wheel while DC24 features Dyson’s Ball technology.

Tools
DC17 comes with a mini turbine head, stair tool, carpet care kit, and low reach floor tool; whereas DC24 comes with a mini turbine head and combination accessory tool.

Bin Capacity
DC17 has a bigger bin.
The bin capacity of DC17 is 0.625 gallons while DC24 has a 0.19 gallon bin.

Weight
DC24 is much lighter.
DC24 weighs only 11.65 lbs while DC17 weighs 20.79 lbs.

Cord Length
DC17 has a much longer cord.
DC17 has a 35 ft cord whereas DC24 has a cord length of 20 feet.

Size
DC17 is larger.
The dimensions of DC17 are 43.5″ x 13.2″ x 16.7″ while the dimensions of DC24 are 29.6″ x 11.0″ x 13.7″ (HxWxD).

Overall, DC17 is full size, and it is very powerful for cleaning large house; DC24 is lightweight and good for small home vacuuming.

Compare and find the differences between DC23 and DC24 below, the better one is the one that suits your needs.
In this post, DC23 refers to DC23 Turbinehead, DC24 refers to DC24 Multi Floor.
Dyson DC23 vs DC24
images from manufacturer

Design
DC23 is a canister vacuum while DC24 is an upright vac.

Cord Winding
DC23 has automatic rewinding function while DC24 doesn’t.

Suction Power
DC23 has much more suction power.
DC23 has a suction power of 220 air watts while DC24 has only 115 air watts.

Motor Rating
DC23 has a 12 amp motor while DC24 has a 6.5 amp motor.

Brushbar Control Type
DC23’s brushbar switch is located on the head, thus you have to bend down to turn it on/off; whereas you don’t have to do this when using the DC24, since it
uses fingertip brush control.

Movement Type
DC23 uses fixed wheel while DC24 features Dyson’s Ball technology.

Tools
DC23 comes with a stair tool, crevice tool, and brush tool; whereas DC24 comes with a combination accessory tool.

Bin Capacity
DC23 has a bigger bin.
The bin capacity of DC23 is 0.44 gallons while DC24 has a 0.19 gallon bin.

Weight
DC24 is much lighter.
DC23 weighs 19.5 lbs while DC24 weighs only 11.65 lbs.

Cord Length
Both have short cord. However, the cord length of DC23 is a bit longer.
DC23 has a 21.6 ft cord whereas DC24 has a cord length of 20 feet.

Size
The dimensions of DC23 are 13.9″ x 19.3″ x 11.9″ while the dimensions of DC24 are 29.6″ x 11.0″ x 13.7″ (HxWxD).

Both of the two vacuum cleaners are priced at $399.99 at Dyson.com (prices checked on August 8, 2011), certified asthma and allergy friendly, come with lifetime washable HEPA filters, and carry 5 years warranty.

Overall, if you live in a small apartment, or want a light vacuum that is easy to carry, compact for storage, then DC24 can get the job done. Otherwise, go with DC23, because it has stronger suction and larger bin.

Compare and find the differences between DC23 and DC25 below.
In this post, DC23 refers to DC23 Turbinehead, DC25 refers to DC25 Multi Floor.
Dyson DC23 vs DC25
images from manufacturer

Design
For design, they are completely different. DC23 is a canister vac while DC25 is an upright. Generally speaking, a canister is a better choice for hard floors while an upright vacuum works better on carpets.

Brushbar Control Type
DC25 uses fingertip brush control, that means you can turn on/off the brushbar without bending down; whereas you have to bend down to control the brush bar of DC23 because its switch is located on the turbine head.

Movement Type
DC23 uses fixed wheel while DC25 features Dyson’s Ball technology. Which is better? It really depends. Some users said the Ball technology makes it easier to maneuver while others said the fixed wheel is more comfortable.

Tools
DC23 comes with a stair tool, crevice tool, and brush tool; DC25 comes with a stair tool and combination accessory tool.

Bin Capacity
DC23 has a bigger bin.
The bin capacity of DC23 is 0.44 gallons while DC25 has a 0.31 gallon bin.

Weight
DC25 is lighter.
DC25 weighs 16.12 pounds while DC23 weighs 19.5 pounds.

Cord Length
DC25 has a longer cord.
DC25 has a 24.6 ft cord whereas DC23 has a cord length of 21.6 feet. However, they are both too short for a large house.

Cord Winding
For DC25, you have to rewind the cord manually, whereas DC23 has automatic cord recoil system.

Size
The dimensions of DC23 are 13.9″ x 19.3″ x 11.9″ while the dimensions of DC25 are 42.4″ x 12.2″ x 15.4″ (HxWxD).

Price
DC25 is more expensive.
DC25 is priced at $499.99 while DC23 is priced at $399.99 at Dyson.com (prices checked on August 8, 2011).

These two Dyson vacuum cleaners both are certified asthma and allergy friendly, come with lifetime washable HEPA filters, and carry 5 year warranty.

The DC25 is selling better than the DC23. But if you have mostly hard floors, go with the DC23. There is higher chance of scratching your bare floors by using an upright.