I have played a lot of tube screamers in my day and the one that I found that I most like is oddly enough the TS10. It would be swell if any tube screamer fanatic know what made the ts10 different from the others.
Here is more than you ever wanted to know about the various tube screamer models:
http://www.geofex.com/article_folders/tstech/tsxtech.htm
Have fun!