Very important question . . .
My dad and I have used Stearns float coats for years, buy them a bit large for fitting over your waders and woolies. I have shot out of canoes while jump shooting, a layout boat, and even while shore hunting over decoys. They are warm, safe, and the 3/4 length keeps your butt warm and they have deep pockets for extra shells, calls, snacks, etc.
Here is my pfd story:
New Year's Eve day of '06 I was hunting the late duck/goose opener in SW Michigan and was paddling out after a slow morning. I jumped a flock of whistlers and took two out of the flock; one dead when he hit the water and a hen with a broken wing. In the process of chasing down the cripple, I managed to reach to far with my paddle and rolled the canoe (water in mid 30's, air 37 with freezing rain starting to fall). "Well," I said to myself,"you really did it this time." I slid back into the canoe, unloaded the gun, laid it in the bottom of the canoe, and reviewed my options.
1) Swim to the nearest shore, about 20 yards away, and then walk around the lake to my car (3/4 mile through muck and mire)
2) Swim to the downwind shore close to the access site and my car (100 yard swim and a short walk to the ramp).
3)Sit there thinking about it until hypothermia did me in.
I pulled my wool hat down tight, adjusted my wool gloves, grabbed a paddle, rolled on my back, and keeping my arms tight to my sides, "paddled" myself to the access site. Was I shivering when I got to the car? You bet, BUT my core was protected by a wool shirt, pants, and other layers, my head covered by wool, and my legs protected by waders, layers, etc, AND I was wearing a full length floatation coat that protected my body and helped my float without needing to struggle. I am alive today because of that coat, being comfortable in the water, and a healthy dose of continuous prayer on the way to the shore.
As a side note, I wear a similar coat in bright orange at work until at least mid June and start again in mid September. I don't care how warm the air is, the water up here stays cold late and starts cooling again early. If your arms get numb, you are in big trouble in the water.
Be safe, shoot straight.