Short answer is the one that fits you the best, and the only way to figure that out to try as many as you can. Your budget is a big factor too, but since you said "best" check out Kifaru, Exo, Stone Glacier, Seek Outside. Any of these can probably get you fitted. There are cheaper alternatives with varying downsides that would be plenty adequate, but the big thing is that what you get needs to fit.
As far as capacity, my Exo 4800 is just about maxed out with everything in it plus five days of food, but my synthetic quilt eats up a lot of pack space. So your gear will help determine capacity. When in doubt, go a little bigger. Most of the really good packs compress down well so there's really no such thing as too much bag, especially once you've packed in overnight gear. I'd probably start at 3000 cubic inches and larger.
Unfortunately, there's no easy answer and no one size fits all answer, at least in my experience. I had to go through a handful of packs to get it right for me.