Hi L.,
They're a little expensive, and I'm usually quite money conscious, but I've found the BabySmart Cooshee Booster Seat (Hybak) worth the money for both my boys. They're safe, durable and really comfortable for them and it's the ONLY booster than my 2yo will sit in. (We had a few from my older son, including a portable one, that he refuses to sit in.) Plus there is room to grow in them. My almost 5 year old uses one also and will probably continue to for a few more years.
The only possible downside to it is it doesn't have any kind of seat belt, but at 2yo+, we don't find them necessary. That might be different for you though, so it was something to mention.
I've heard people that like the Kaboost too, but it wouldn't work for us because my 2yo likes to be able to get in and out of his seat by himself, and it seems that the Kaboost would make his seat too tall to do that. I'm not sure about the extra height for falling too. Could be ok though - I just don't know.
Good luck!