According to Hoover customer service and info on Hoover.com, the difference between Hoover Air Cordless Series 1.0, 2.0 and Series 3.0 are:

1, Headlight.
Hoover Air Cordless Series 1.0 has NO Headlight while the series 2.0 and 3.0 feature LED Headlights to illuminate dark spots for a thorough clean.

2, Included Tools.
The series 1.0 comes with the 2-in-1 Cleaning Tools (dusting/crevice);
series 2.0 also has the 2-in-1 Cleaning Tools;
the series 3.0 not only includes the 2-in-1 Cleaning Tools, but also comes with an Additional Filter that you can use when the other one has not been dried yet, a Hard Floor Brush Roll for cleaning bare floors, and a Pivoting Dusting Tool to clean hard to reach areas.

3, Where Sold.
Hoover Air Cordless series 1.0 (BH50100, BH50100CDI) sold at walmart.com and canadiantire.ca;
2.0 (BH50110) sold at target.com;
3.0 (BH50120, BH50121, BH50140, BH50150) sold at Hoover, BestBuy, HomeDepot, HSN, Amazon, Sears, Kohl’s.

4, Price

1.0 is priced at $258.96 on walmart.com
2.0 is priced at $269.99 on target.com
3.0 is priced at $299.96 on hoover.com
(prices checked on June 23, 2014)

The difference between Hoover SH20030 and S2220 are:
Hoover S2220 vs SH20030
images from manufacturer

Price:
The Hoover SH20030 is a bit more expensive, it is priced at $64.99 whereas the S2220 is priced at $59.99 at hoover.com (prices checked on July 13, 2013)

Edge Cleaning:
The SH20030 features Brushed Edge Cleaning that removes dirt and dust up against edges whereas the S2220 does not.

Height Adjustment:
The S2220 has 3 manual height settings whereas the SH20030 features automatic adjustment.

Filtration:
The SH20030 uses Micro filtration while the S2220 use standard filtration.

Hoover WindTunnel Technology:
The SH20030 features Hoover WindTunnel Technology while the S2220 does not.

Warranty:
The SH20030 is backed up with a 2 year limited warranty while the S2220 carries 1 year limited warranty.

Nozzle Width:
The SH20030 has a nozzle width of 11 inches while the nozzle width on S2220 is 9-inch.

Color:
The SH20030 is grey while the S2220 is red.

Similarities:
They are bagless.
They both have spinning brush and brush on/off switch.
They have 20 ft cable.
120 volts motor.

Read manuals for more details:
SH20030 manual: http://hoover.com/file/642/
S2220 manual: http://hoover.com/file/617/

If you know more difference between Hoover S2220 and SH20030, please share here, thank you.

The difference between Hoover S2220 and S2200 are:
Hoover S2200 vs S2220
images from manufacturer

They are in different colors.

The S2220 has a motorized brushroll that can be turned off whereas the S2200 does not have a beater bar.

On hoover.com product pages, it states that the S2220 has a 8.2 amp motor while the S2200 has a 6.8 amp motor.

The S2220 is a little more expensive than the S2200, it is priced at $59.99 whereas the S2200 is priced at $49.99 at hoover.com (prices checked on July 12, 2013)

Otherwise, they are identical.

They are bagless, have no bag to change.

They have 20 ft power cord.

They feature slot for hanging up.

They carry one year limited warranty.

120 Volts.

3 level height adjustments.

9-inch Nozzle Width.

They have no attachments, no headlight, no speed settings.

Learn more by downloading manuals:
Hoover S2220 manual: http://hoover.com/file/617/
S2200 manual download: http://hoover.com/file/618/

If you know more difference between Hoover S2200 and S2220, please share here.