It depends, I have a pack but it is hot, heavy, and bulky. I also have a vest which I also combine a good amount of the time with a think tank belt and cotton carrier holster.
I use the backpack or belt (with or without the vest) about 50/50. The backpack is nicer for carrying lenses and bulky stuff but has the drawbacks of being hot, heavy, bulky, and if you're constantly working out of it you gotta take it off to get to anything. The vest is much nicer to me to work out of because everything is right there, no taking it off to have access to anything. Its also cooler and you can really weigh it down and not feel it too much because the weight is distributed over your entire body. Its not as well suited to carrying bulky stuff like lenses though (even though you can, mine has pockets big enough to lose a 70-200mm f/4L in.
The think tank belt and cotton carrier are the best things I've ever come across, I just need to get around to getting an adapter plate so I don't have to constantly switch back and forth from my cotton carrier button to my tripod plate. No neck straps for me, no cameras bouncing around smacking me in the chest and swinging all over the place putting strain on my neck. Camera sits right on my hip until I need it. I don't believe you can buy just the CC holster anymore though, I think you have to buy the whole package. I will be buying more of the think tank components to go on my belt though (along with some of their suspenders) to put gear in which will probably mean I'll use my backpack even less.
If you're looking at a belt system look at Think Tank, you'll pay for their stuff but its really well made.
