The Shinano looks good but one thing I like about the Ospreys are the webbing on the back panels and the sausaging of my Mule is another reason I was straying from anything without an internal frame.
I think I'm going with the Synchro 15. Manta 20 is nice but it may be too big for my daily rides.
I use(d) an Unzen 6. In my opinion, that's the largest size that design works really well with. It's large enough to hold two spare tubes, wallet, phone, keys, multi tool, pump, and room to spare for food and a couple of layers. The material is very stretchy, and expands quite a bit. The Source bladder is easily better than CamelBak or Osprey, since the top can be opened entirely for easy cleaning–no brushes/hoops to jump through to dry it out, either.
I like the strap arrangement better, too, since I have a separated AC. The smaller size don't need a waist band that impedes good breathing, either. Even filled up, the 6 doesn't flop around, since most of the weight is in the small of your back. IMO, the only reason to step up to the 10+ is it you want carry loops on it, but 6" of tubular webbing, a sewing machine/awl (or a friend with one), and 5 minutes solves that problem.
I used to use a CamelBak Alpine pack, but that is in a whole different category (medium/large daypack with loops for trekking poles/axes, etc).