thunderbird and fullerplast should you want to spray the finish on work wonderfully. These are probably the 'best' but are typically sprayed on.
Should you want an easy finish, the water based polys work well - though less durable than those listed above - and probably less waterproof as well. Wipe on or spray cans work fine. I prefer the spray can and the rougher finish it provides.
Massie finish (epoxy and acetone) works well, is easy, is waterproof, but takes time any many coats. (and it's quite shiny if not dulled)
thunderbird and fullerplast are probably the best if you have the equipment or want to spend the money on the equipment.
I'm not in the rain that often, and usually shoot bows in my range at home, and so mine usually end up with a spray on can of poly.
Whatever suits you intended application best.
Aaron