I use the ultraspire surge but take the bladder out. Its enough room for everything that I need to carry and for mandatory kit.
I am tempted by the Ultimate Direction signature vest... the Anton Krupicka one.
With regards to one bottle, I guess its personal preference. I only carry one as I find that is enough to see me through about 20 miles if need be.
Edited: 04/01/2013 at 20:06