I've worn the Float 22 that Missy shows there, the newer version coming out this year and the Float 25 this past winter. The most versatile of the group is the 25. External shovel pouch, pull cord on the right side (but can be moved) and an adjustable waist strap that allows you to move it up and down depending on the length of your torso.
With all this said, BCA is coming out with a Float 8 that is minimalistic, small for small frames. Just no storage.
I have a ABS SB 15 - it fits my small frame and allows me to move freely - riding trees requires lots of movement (especially for me as a small person) and so that was a big concern of mine before getting it.
What sold me on the ABS Avalanche bag was witnessing one of our riding buddies getting caught in an avalanche and burried - the ABS has two bags that inflate and one of them did not inflate while the other one was enough to keep him afloat or close enough to the surface that his hand was sticking out so it was a very quick and easy recovery!
If he had a pack with a single air bag and it did not inflate for some reason, he'd very likely be dead as it was a deep avy and could have easily taken us longer than 10 minutes to get to him if we had to dig through all that debris to it's lower depth.
I actually wrote and article on this occurrence and have many photos on it as well as a diagram - check it out here: