Its a very hard decision between the two. I've even battled back and forth before picking up a 2.4Ghz 13" macbook pro (sold it off though, cant stand the glossy screen!).
11.6" vs. 13"
thin vs. less thin
1.4GHz vs. 2.4Ghz
Semi-glossy vs. Glossy
I am actually thinking about picking up a mba.