The 2.9% + 0.30 model seems to be pretty drilled into everyone's head... it's worth noting that if you get a real merchant account from a company like Chase Paymentech or First Data... you'll get pricing as low as like 0.05% for debit cards (w/ interchange plus). All in all, it would average to around 2% or less per card you process. If you do any kind of volume - it's worth it.
Braintree's checkout process is every bit as easy to implement as Stripe's. However, signing up for Braintree and getting approved takes longer (at least in the EU - I don't know what the situation is in the US). On the plus side, Braintree works in several countries that Stripe doesn't yet work in.