Dyson DC50 and DC44 suit different needs.
The key difference between them is the DC50 is corded while the DC44 is cordless. What’s the point of this?
The DC50 is more powerful, but its short cord limits the area you can vacuum, thus you might have to switch outlets constantly.
The DC44 is lighter and have better portability, but the battery life and charging time may be something you should consider.

Compare Dyson DC44 and DC50 Animal

	Dyson DC50 Animal	Dyson DC44 Animal
Images
Price	$449.99 at dyson.com on July 18, 2014	$399.99 at dyson.com on July 18, 2014
Cyclone Technology Type	2 Tier Radial™ Cyclones	Root Cyclone™ technology
Ball Technology	Yes	Yes
Design	Compact Upright	Stick/Handheld
Corded or Cordless	Corded	Cordless
Cord Winding	Manual	NA
Cord Length	24.9 feet	NA
Battery Type	NA	22.2 volt Lithium ion
Battery Life	NA	20 minutes on standard mode or 8 minutes on boost mode.
Charge Time	NA	it takes about 3.5 hours to fully charge
Docking Station	NA	Yes, wall mount docking station for charging, and stores the vacuum and accessories.
Suction Power	128 airwatts	28 airwatts at Standard Power or 65 airwatts in Boost mode
Bagged or Bagless	Bagless	Bagless
Bin Size	0.21 gallons	0.09 gallons
Motorized Head	YES	Yes
Brush On/Off	YES	No
Cleaner Head Width	about 11″	about 8.25″
Manual Pile Adjustment	No	No
Weight	11.6 lbs	5.07 lbs
HEPA Filtration	YES	not specified
Included Tools	Tangle-free Turbine tool Combination Tool Stair Tool	Mini motorized tool Combination tool Stair tool
Dimensions	30.1" x 11" x 13.9"	44.1" x 9.1" x 11.8"(HxLxW)
Warranty	5 year warranty on parts & labor	2 year parts and labor warranty
User Guide	Dyson DC50 Animal Manual	Dyson DC44 Animal Manual

If you are tired of the limited battery life? Then choose the DC50.
If you want a more portable unit that can do quick pick ups and get under furniture? Then go with DC44.