I've used everything from a vest, chest, and hip packs. For years after shoulder surgery I used a hip pack for trout fishing with a single hand rod. I typically use a vest for that type of fishing now - but I try to keep the contents minimal, if I can. For swinging flies, I prefer a hip pack - mine is a waterproof zippered Simms. I can wade deep with it and contents stay dry. I like the freedom of movement in the shoulder area with a hip pack when using a TH rod. I've not tried a sling - mostly because I prefer to evenly distribute the weight on both shoulders. When I'm out all day steelheading far from the truck, I take a waterproof roll top day pack (Patagonia - but lots of others out there too) - never gotten wet inside even in some damn nasty all-day rain/snow. I can carry a rain jacket, extra layer, gloves, lunch, water (or hot water for tea in cold weather) in the pack. It even fits my hip pack. Like Ambest, I usually drop the day pack on the bank and don't fish with it on.