You may want to check out this link. It allows you to compare many devices side by side http://www.blackberry.com/compare/index.do
We have a mix of 7520s and 7130s, and 7100s. I've deployed a few of the 7100s over the past couple of months and I like my 7520 better.
- Keys farther apart for my fat fingers
- No multitap for typing - I hate needing to hit a key twice to type one letter
Having said that, the screens on the 7100s appear to be a bit brighter and at the risk of sounding shallow, I have to say it's got a 'sexier' feel in the hand. If you send a lot of e-mail, stick with a model that's got the full keyboard. It not, the 7100 is nice. If I had to give up my 7520, I'd go with a 7130. Just my 2 cents...