If price doesn't matter buy from Apple.com.
Crucial has sort of a bad rep around here, though, since they use variable pricing or some nonsense where different people see different prices. I don't know if it's something they've stopped, but there are quite a few angry threads about it.
I got all my ram from DMS (datamem.com) or newegg, though that's a bit of a risk as far as compatibility goes.
How much warrantee do you get from both companies on the RAM?
If price doesn't matter buy from Apple.com.