The main difference between Hoover UH70120 and UH70825 are the versions of WindTunnel technology they feature and color.
As you can see from the product name, Hoover UH70120 utilize WindTunnel technology while UH70825 features Windtunnel 2.
And the position of the ON/OFF switch is different. On/Off switch on the UH70120 is located on the handle that is easier to reach while the switch on the UH70825 is located on back of the unit.
For those who like the retractable cord, these 2 vacuum cleaners fit your needs, both of them have the cord rewind system.

Compare Hoover UH70825 and UH70120

	Hoover UH70120 WindTunnel T-Series Rewind Plus Bagless Upright Vacuum Cleaner	Hoover UH70825 WindTunnel® 2 Rewind Bagless Upright
Design	Upright	Upright
Price	$129.99 at Hoover.com on July 26, 2014	$129.99 at Hoover.com on July 26, 2014
Bagged or Bagless	Bagless	Bagless
Dirt Bin Capacity	not specified	not specified
Bottom-Release Bin	Yes	Yes
Cord Length	27 ft	25 ft
Auto Cord Rewind	Yes	Yes
Amps	12 Amps	12 Amps
Motorized Brushroll	Yes	Yes
Brushroll On/Off	No	No
Height Adjustment Type	Manual, 5 Settings	Manual, 5 Position Height Adjustment
Washable Filter	Yes	Yes
HEPA Filtration	Yes	Yes
Headlight	No	No
Weight	16.5 lbs	17.4 lbs
Cyclonic Action	Dual	Dual-Cyclonic
WindTunnel Technology	WindTunnel	WindTunnel 2
Performance Check Indicator	Yes	Yes
Nozzle Width	13.5"	13.5"
Edge Cleaning Brush	No	No
Self-propelled	No	No
Handle	D-Shaped Handle	D-Shaped Handle
Deep Recline Handle	No	No
Hose Type	stretch hose	stretch hose
Hose Length	8'	8'
Included Tools	Air Powered Hand Tool, Crevice Tool, Dusting Brush, Upholstery Tool	Air Powered Hand Tool, Crevice Tool, Dusting Brush
Cleaning Wand	Yes	Yes
Color	Gray and Green	Black
Warranty	2 year limited warranty	2 year limited warranty
Manual	download manual	download manual

Both of them do not have the switch to turn off the brush bar, when you want to vacuum hard floor, you can adjust the dial to bare floor setting.