Here’s a chart that shows the features you will have with iOS 5 on the 1st, 2nd and 3rd generation iPads. Of course, since the first iPad did not have a camera you will not have features like FaceTime, Photo Booth and photo editing.
The only features missing from the second generation iPad is the ability to use it as a personal hotspot (which is not supported by all carriers) and Dictation.
It’s also worth noting that the iPad 1 does not support Smart Covers, while both the iPad 2 and iPad 3 have embedded magnets that make the Smart Cover snap in place and turn off and on when the cover opens and closes.
iPad 3 vs iPad 2 vs iPad 1
This is only a partial list of iOS 5 features but the remaining features should be accessible on all iPad versions.
Refurbished fist generation iPads can be purchased from the Apple Store starting at $299. New iPad 2s start at $399 and refurbished ones start at $349. If you want the new iPad (3rd generation) you will need to spend at least $499.
You will want to weight out the features and prices to determine the right iPad for you.