3 columns all the way. I switched a while ago and can't look back now. I just recently cracked my 920 and went to a TMo store today to check the 635 to see if it would feel like a huge downgrade: nope, not at all. Sure some apps open slower but it's barely noticeable. Also, the screen! I'm very impressed, it is
clearly better than my 920's screen, it has much deeper color quality and most impressively, I barely noticed the lower resolution. Actually I didn't notice any lesser quality, period.
My only freakout was that I was unable to switch to the 3 column style but after reading this thread it seems that must have been the store phone model which may be limited in some demo ways... I thought it could do 3 columns simply due to it's screen size, and you guys obviously confirm that. I may very well order one tonight. For reference, this is what my 920 looks like right now... :/