I've got all three items, vest, chest, and rump (fanny pack), and use them at different times. I wear the rumper when it is hottest out or when I need to carry the least gear. I like the chest pack best, overall, but I find it sticks my shirt to me when its hot and keeps the breeze from blowing it about. I use the vest when needing to carry obnoxious amounts of flies and/or when needing extra jacket(s).
The chest pack I got is the William Joseph Gear Bag Chest. The thing was pretty **** expensive, but has lots of really well thought out features. I keep a hydration bladder in the back, and its tube slips nicely into one of the shoulder straps. The length of the straps are adjustable and the adjustment is cleverly concealed within the back of it. It has a great tippet dispenser on the front of it and tons of ideally sized pockets. You can undo the side straps and spin it around to access the stuff in the back without having to take it off as well. Steve's shop, www.thefullcreel.com
sells them. Just for the record, I didn't do that great big long write up just because Steve sells them. I bought the thing months before I knew of this forum or his shop.
There's lots of others out there with similar features and benefits. I would recommend looking into a setup than can be used just as a front of chest pack as well as a more capacious front and back set up. The double haul thing from Fishpond looks great. Steve sells that too.
For something much cheaper, Loon's Idaho Chest Pack looks great too. Yep, Steve sells them.