If it has to be a zoom, the 100-400 is, in my opinion pretty good. It doesn't compare to a prime, but it'sa zoom! Certainly better than a 70-200 with a 2x teleconverter. I did that a couple times, EVER. Was not happy with it at all. I was actually kind of pissed off. Bryan said it wasn't that great, but I had to learn for myself...