I use a....
...waist pack during the summer due to it's ease of use when getting in and out of the car and the stream, being so compact. I also use a Fishpond Goretex which is kind of a cross between a vest and a check pack. It has some mesh, so it's is a bit cooler temp wise than a standard vest and it will haul more than i could use in a lifetime.
I did have one problem and complaint about thje Fishpond as others also mentioned about having with their packs. The abundance of zipper pulls seemed like they were almost magnectic, pulling the tippet on my line into the small gap the oulls were tied through. I modified this by using some "Loon Knot Sense" and put a dab of it over the gap in the zipper then activated it with a UV light. It seems to have eliminated the problem with snags on my chest pack.
"Fly-fishing has many attributes, but none more pleasing than it's ability to liberate the young boy that still hides within me and to let that boy live again without embarrassment or regret, sorrow or anguish." Harry Middleton