I like a traditional vest during peak season, just because you can carry, more, fly boxes, easier, then in a pack. Most of the year I use an older Sage guide bag; if you've seen the newer fishpond shoulder strap bags same thing. It has two main, zipperd, comparments and lots of pockets inside..I can fit an assortment of boxes, camera, sunglasses, leader/tippet and much more in there..When I'm done fishing for the day just take it off and throw it on the front seat..
I prefer the shoulder strap bags over all because:
1) small compact, yet can hold a lot of gear..
2) light weight better for Summer fishing..
3) Budget and value, good vest set you back a least 100. bucks..Bag only $50-70
and more..
I forgot what they're called but if you go to fishpond I'm sure you'll find them there..If I were in the market right now I'd get the fishpond...