My friend and I had the debate between the 13" vs. 11". He ended up getting the 11" and for myself I got the 13".
He went for the 11" cause he liked the screen better was what it came down for him. He also opted for an i7 upgrade and kept the memory the at 4GB. The screen actually has more room for programs as it actually has a higher DPI than the 13".
I went for the 13" because it is a bigger screen. I also decided that the battery life was better and more important in my decision. I opted for 8GB of memory instead of 4GB as it was a $90 BTO instead of the i7 which gives you at most a 17% performance gain in some tasks. I sometimes run memory intensive applications at once.
I usually run either a programming app (Xcode, Netbeans, Coda), browser (Chrome or Safari), media player (either inside browser via Pandora, or Plex or iTunes), Evernote (or another some kind of word processing), Rulers (so I can work with pixels a bit easier when coding), Mail (it is an app I always have running and begins at login), System Pal (for monitoring, again starts at login), DropBox (again starts at login), Caffeine (again starts at login) and Reminders (again starts at login).
Running all that I don't hit 4GB of memory but come very close to it and I rather not have paging waste valuable SSD space or having waste SSD cycles.
It's up to you, if you can get your hands on both to try them out then you should do it because you don't have to satisfy us here at MacRumors. The only persons opinion you need to justify your opinion to is yourself because if you aren't happy with it, then why buy it?