J.N.
Well, we are crazy and have both. My daughter got the Leapster at 3 and the Tag at 4. I wish we had the new Tag that holds 10 books rather than 5, but oh well. She LOVES her Leapster. She likes the Tag and I truly believe that it helped her learn to read. Now that she is reading, she doesn't play with it as much. I like the Tag better because although the Leapster is educational, it really is just a video game system and the Tag is really reading with phonics games and comprehension questions.
We do reserve the Leapster for things like long car rides, waiting rooms and her little brother's nap time! For those things, it is a life saver!