The difference between Hoover UH30300 and UH30310 are:
Hoover UH30310 vs UH30300
images from manufacturer

Standard VS Pet:
The Hoover UH30300 is a standard model while the UH30310 is pet model.
Pet model features Activated Carbon to absorb pet odors and other household odors whereas the standard model does not have.
Pet models have tools that are designed for pets, the air driven pet hand tool and the pet upholstery tool feature rubber wipers to help remove pet hair from furniture and upholstery. While the tools on standard models do not feature rubber wipers.

Hose: The UH30310 has a longer stretch hose.
The UH30300 comes with a 8 ft stretch hose whereas the UH30310 has a 12 ft deluxe stretch hose.

Price: The UH30310 is $10 more expensive than the UH30300.
The UH30310 is priced at $149.99 at hoover.com whereas the UH30300 is priced at $139.99 (prices checked on July 7, 2013)

Other than that they are almost the same.

They are T-Series Windtunnel bagged upright vacuum cleaners.
They feature Brushroll Shutoff that allows you to use it on bare floors without the risk of damaging the floor by the spinning brush.
Equip with Headlight to illuminate dark areas for thorough cleaning.
Full Bag Indicator to tell you when to check bag and filter.
5 Level Height Adjustment that allows you to adjust to clean different flooring types.
Feature D-Shaped Handle.
Weighs about 15 pounds.
Equip with 12 amp motor.
Have a 30-ft cord.
13.5 nozzle width.
HEPA media filters traps more than 99.9% of tiny particles down to 0.3 microns.
No cord rewind.

You can learn more by downloading the manuals:

UH30300 manual
http://hoover.com/file/543/

UH30310 manual
http://hoover.com/file/544/

If you know more difference between Hoover UH30310 and UH30300, please share below.

Below are the difference between Hoover UH30010com and U5140-900
Hoover U5140900 vs UH30010COM
images from manufacturer

Portable Canister Vacuum:
The UH30010COM comes with a portable canister vacuum cleaner for portable cleaning while the U5140900 does not have such a canister.

Height Adjustment:
The U5140900 has 5 manual height settings while the UH30010COM adjusts height automatically but no manual settings.

Brush Speed:
The UH30010COM has 2 speeds while the U5140900 has only 1.

Full Bag Indicator:
The UH30010COM features full bag indicator while the U5140900 does not.

Headlight:
The UH30010COM features headlight whereas the U5140900 has no headlight.

Bag Type:
The U5140900 use Allergen Media bag that can capture 99% of particles down to 5 microns.
While the U5140900 features HEPA media bag that can capture 99.97% of particles down to 0.3 microns, it gives you better air quality than allergen media bags.

Location of ON/OFF Switch:
The ON/OFF Switch on UH30010COM is on the top of the Handle whereas the one on U5140900 is located on the top left of the vacuum body.

Tools:
The UH30010COM comes with one Telescopic Extension Wand, one Crevice Tool, one Dusting Brush, one Floor brush.
Whereas the U5140900 has 2 Extension Wands, one Crevice Tool, one Dusting Brush, one Upholstery Tool.

Nozzle Width:
Nozzle Width of the UH30010COM is 14 inches while it is 15-inch on the U5140900.

Cord Length: The UH30010COM has a much longer cord.
The cord length on the UH30010COM is 35 ft while it is 25 ft on the U5140900.

Handle:
The UH30010COM features D-Shaped Handle whereas the U5140900 features Standard Grip Handle.

Weight: The UH30010COM is lighter.
The UH30010COM upright unit weighs less than 12 pounds while the U5140900 weighs more than 16 pounds.

Warranty:
The UH30010COM carries 5 year limited warranty while the U5140900 has only 1 year limited warranty.

Price: The UH30010COM is $200 more expensive than the U5140900.
UH30010COM is priced at $299.99 while the U5140900 costs $99.99 (prices checked on July 01, 2013 at hoover.com)

Color:
The UH30010COM is grey while the U5140900 is blue.

Similarities between Hoover UH30010com and U5140-900:
They are bagged upright vacuum cleaners.
equip with motorized brush but no brush On/Off switch;
12-amp motor;
no auto cord rewind.

You can also download the manuals to learn more, here are the links:
UH30010COM manual: http://hoover.com/file/537/
U5140-900 manual: http://hoover.com/file/431/

If you know more difference between Hoover UH30010com and U5140900, please share here.

Hoover T-Series WindTunnel Pet Rewind Bagless Upright Model #UH70210 and WindTunnel MAX Pet Plus Multi-Cyclonic Bagless Upright Model #UH70605 are 2 Hoover pet vacuum cleaners. There are some difference between them, let’s compare below.

Hoover UH70210 vs UH70605
images from manufacturer

Height Adjustment:
The UH70210 has 5-level manual height adjustment while the UH70605 equips with 7 settings.

Color:
The UH70210 is a blue while the UH70605 is grey.

Nozzle Width: The nozzle width on UH70605 is 1.5-inch wider.
The UH70605 features 15-inch cleaning path width while the nozzle width on UH70210 is 13.5 inches.

Cyclonic Air Action:
The UH70605 features Multi-Cyclonic Technology while the UH70210 features Dual Cyclonic Air System.

Hose:
The hose on UH70210 is 8 ft long while the UH70605 has 12 ft long stretch hose.

Weight: Hoover UH70605 is a bit heavier than the UH70210.
The Hoover UH70210 has a weight of 17.8 pounds while the UH70605 weighs 18.4 pounds.
ft.

Cord Length: The cord on UH70605 is longer than UH70210.
The cord on UH70210 is 25 ft long while the cord length of the UH70605 is 28 ft.

Onboard Tools:
The Hoover UH70210 comes with Turbo Pet Tool, 12-Inch Extension Wand, Crevice Tool, Pet Upholstery Tool
While the UH70605 comes with Pet Turbo Tool, 24-Inch Telescoping Extension Wand, 12-Inch Crevice Tool, Dusting Brush, Pet Static Tool

Price: The UH70605 is $10 more expensive than the UH70210.
UH70210 is priced at $159.99 while the UH70605 costs $169.99 (prices checked on June 25, 2013, at hoover.com)

The similarities between them:
equip with headlamp for cleaning low light spots;
have automatic cord rewind system to quickly retracts cord and lets cord store inside the vacuum cleaner compactly.
have HEPA filter;
powered by 12 amps motor;
carry 2 year limited warranty;
indicator light to remind you to dust bin and filter;
have ON/OFF pedal to control the brushroll, you can turn brush on or off to clean different floor types;
feature D-Shaped folding handle that allows you to fold down for compact storage;

You can download manuals to learn details if you like:
UH70210 Product Manual Link: http://hoover.com/file/574/
UH70605 Product Manual Link: http://hoover.com/file/581/

We would appreciate you sharing more info here if you know more difference between UH70605 and UH70210.

UH71209 vs UH71214
images from manufacturer

It seems that there is no mechanism difference between Hoover UH71214 and UH71209 except for the color.
The color on the base of UH71209 is mostly red while the base of the UH71214 is red with black.

The same thing they have:
WindTunnel Technology cleans all floors better;
Multi-Stage Cyclonic Filtration traps dirt and dust before it reaches the filter with no loss of suction;
Washable filter with HEPA Media filter trap over 99.9% of small particles down to 0.3 microns;
25 ft power cable with auto cord rewind provide quick winding and neat cord storage;
Beater bar On/Off pedal makes it a snap to switch between hard floors and carpeting;
5 height settings adjust as needed to vacuum different flooring types;
10 ft stretch hose provides long cleaning reach with wand and crevice tool;
On-Board Tools, a Turbo Tool, 24″ Telescoping Extension Wand, Dusting Brush, Crevice Tool, for cleaning fruniture, lampshades, hard to reach areas, etc.
Have Bumper that protects furniture;
System Check Indicator light to remain you when the filter and dirt cup need to be checked;
13.5-inch cleaning path;
Weighs 18 pounds;
12 amps motor;
D-Shaped type handle;
Dual Cyclonic Air System;
limited 2-year warranty.

Do you know more difference between UH71214 and UH71209? If yes, we would appreciate you if you could share info here.

These are 2 Hoover vacuum cleaners for pets, the difference between Hoover UH70085 and UH70210 are:

UH70210 vs UH70085
images from manufacturer

Handle:
The Hoover UH70210 equips with a folding handle that allows you to fold it down to store neatly while the handle on UH70085 is unfoldable.

Nozzle Width: The nozzle width on UH70085 is wider.
The UH70085 features 15-inch nozzle width while the UH70210 has 13.5 inch nozzle width.

Product Weight: Hoover UH70085 is heavier than the UH70210.
The Hoover UH70210 weighs 17.8 pounds whereas the UH70085 weighs 22 pounds.

Cord Length: The UH70085 has a longer power cord.
The cord on UH70210 has a 25 ft cord while the cord length on UH70085 is 28 ft.

Warranty:
The UH70085 carries 1 year limited warranty while the UH70210 has a 2-year limited warranty.

Color:
The UH70210 is a blue while the UH70085 is red.

Price: The UH70085 is $40 more expensive than the UH70210.
UH70210 is priced at $159.99 while the UH70085 costs $199.99 (prices from hoover.com, checked on June 24, 2013)

The similarities:
headlight for vacuuming dark corners;
eight feet stretch hose;
height adjustment with 5 settings
auto cord rewind to retracts cable automatically and allows cord stores neatly inside.
come with pet hair cleaning tool;
equip with HEPA filter to better air quality;
bottom empty dirt cup;
powered by 12 amps motor;
system check indicator to warn you to check filter and dust cup when it is needed.
beater bar can be shut off by touching a foot petal for cleaning bare floor.

To learn details, you can download:
UH70210 Manual: http://hoover.com/file/574/
UH70085 Manual: http://hoover.com/file/561/

We would appreciate you sharing info here if you know more difference between UH70085 and UH70210.