FTV has the most bodybuilders and perhaps the most overall models. They focus on shooting at big shows so they have the most "name" models. My critisism is that their picture and video resolution isn't very high. If it wasn't for that I might give the win.
Muscle Angels doesn't have the volume of material that the others have because it hasn't been around as long, but they have high quality "name" models including quite a few that are rare elsewhere. The pictures and videos are first rate.
HerBiceps has a lot of no-name models that aren't particularly muscular. They have a large amount of fitness competitors, but not too many bodybuilders. The pictures and videos are first rate and they probably produce the greatest volume of material on a weekly basis of any site and have an archive comparable to FTV.
I'll throw in HD Physiques as a fourth. HerBiceps and FTV are the titans battling it out. This site is more on the level of Muscle Angels. I recently re-joined them and I had forgotten just how much material they actually had. If you appreciate Canadian competitors, this is the place to see them. As the name implies, they have excellent picture and video resolution.
If you've never been a member, any of these sites will keep you busy mining the archives and provide enough material to make them worth at least a month. Personally I maintain memberships on three of them, because somebody has to pay for the fine work that these photographers are doing and to ensure that there will be new material.