It's a toss up for me. I would say it runs 50/50 for my EF 85mm f/1.2L or my EF 135mm f/2.0L. They both are great. I'm looking at the 200mm f/2.8L and am dreaming about the 300mm f/2.8L (but ~$4200 is a bit much for me)... Maybe I'll pick up a 5D or it's successor first.