I've always used a vest when trout fishing. I bought an Orvis sling pack when they first came out and after a few trips with it just didn't like it. With my vest I am more organized and know where everything is. Surprisingly I don't carry a boat load of stuff and my vest is very light. For warm water I use either a Recycled Waders Big Fanny or a Woodstream bag.

I think older guys, like me, who started our using a vest tend to stick with them. Mine is a Fishpond Sage and is very comfortable. Younger guys seem to prefer sling, fanny or chest packs.