I like 3, 7, and 8 for some reason (and whatever number they are with, like 13, 18, 88 etc....). And they remind me of the colours purple and lime green, which are my favourites.
I'm a little like Mystyfyr: mine is e because in my education, the damn thing shows up all over, when you least expect it, and does such unique things as well. And of course because it's a key player in: e^(pi*i) +1 =0, the most elegant formula in the known universe.