Welcome to the forum. I have a Trek 7200 and my wife has a 7100 that we are very pleased with. We ride the Chicago lakefront, numerous bike paths, etc. quite a bit and love it. You will get a lot of advice here - no doubt. (The comment re: front suspension, I respectfully disagree...I find that it doesn't hinder/slow us down etc. at all - and when you hit a 'bump in the road' it helps a good deal - especially with bad shoulders/arthritis etc.). Best idea of all - go visit a bunch of LBS (Local Bike Shops) - try a bunch of different models and buy the one that YOU like - eventually you'll be hooked and will want to start adding some stuff - like a rack/bag, maybe some ergonomic grips, a mirror, water bottle holders etc. I read somewhere that "now" (or at least in the next few months is an ideal time to buy, as there are some deals to be had on 2010/11 models as the new inventory is coming in). I believe that any of those bikes you list are more than capable of helping you with your knee and getting up and out there - have fun!!!! Welcome - would be interested in hearing what you end up with and have a great Holiday.