RE: 3-9 or 2-7 or 1.5-6 power scope for muzzle loader?
I would opt for the 2x7x33 given the ranges you describe. Keep the scope on the 2X if most of your shots will be in the 30-40 yard ranges. It's nice having the option to go 5-7x when you are out at 100-130 yards.
I have a 1.5x5x32 on my Omega. I had a few deer in the 200-225 yard ranges last year and they looked tiny on 5X. Even if I had a beefy scope on top I would of passed as they were small body deer.