I have to say I think the palm axis is the business, it's not too big- I used it freestyling on the nile- it's good and solid, and i really love the big pocket- I can fit a sling, three crabs, knife, two prusics, scull cap, food, and still have some room- that's pretty much a pin kit and extras on me all the time. It'll probably take a while but palm are starting to change the foam in their ba's to the same stuff windsurfers use- overtime it molds into the shape of your body for a better fit.
I find the astral too small and can't carry all the kit I want, and the serpent only has one strap around the middle- which means if you ever have to release the cowtail you only have the two bottom straps and shoulder straps keeping the BA on you.