I own several chest packs and several vests.
For backcountry trips where I'm covering a lot of miles and weight is at a premium, I just take a fishing shirt with lots of pockets, and a William Joseph Ultralight chest pack (only 5 ounces.)
William Joseph Ultra Light Chest Pack
For day trips or backcountry fishing trips where I'm not sawing the handle off of my toothbrush to save weight, my go to "vest" is a fishing pack, specifically the LL Bean "Rapid River" pack.
Rapid River Vest Pack: Fishing Vests at L.L.Bean
Why I like it:
It is the only vest/chest pack I've found that will hold a hydration bladder full of water. Other vests and chest packs are supposedly designed to hold a water bladder, but I've found that when you are wearing them, the weight of the water causes the vest/pack to droop down in back and ride up in the front, causing discomfort and a poorly fitting pack. (The William Joseph Fusion vest has this issue, in spite of the fact that it is touted as designed for a hydration bladder."
2) Waist Belt:
The waist belt gets the weight off of your shoulders, and also gives great support for your lower back when you are on the river all day. Some folks wear a separate lumbar belt for back support. It's not necessary when wearing this pack.
3) Accessory sleeves:
Every vest or pack these days has retractable "zingers" or bungies or the like to hold your nippers and hemostats. However, very few vests of packs have little sleeves to insert the tools into to keep them from flopping around. The LL Bean pack has both the zingers, and also some nice little sewn sleeves that keep the tools secured when not in use. They are immediately accessible, but don't flop around when wading.
4) Good pockets:
Fly box pockets are big enough to hold 2 regular fly boxes or one of the monster boxes. There's enough storage elsewhere to keep floatant, tippet, strike indicators, etc. close at hand.
5) Expandable storage:
There is an expanding rear pocket that can get big enough to store rain gear lunch, etc.
At $99, it's a bargain, considering what you get.
My only discontent with this pack is that there is no built in fleece patch for drying flies.