I prefer "Toploaders". I use, both, a Lowepro Topload Zoom AW ( similar to their S&F Toploader 75 AW), and when I wish to carry additional gear, a Specialist 85 AW. With either of these "Shoulder / Belt"--combo bags, I can carry a 20D/BG-E2D, with 100-400 L IS lens attached, and ready to shoot.
Works well with a "Grip Strap" ( I use a Zing).
These bags wont take "the" setup with the Canon hood extended, so I use it with a collapsible rubber hood attached, and I haven't experienced any notable flare problems.
Note however, that even the Specialist 85 is somewhat limited to the amount of gear it will hold--- The Camera/100-400 L, and 1-2 smaller lenses, plus a flash is the limit!