That Zeiss Conquest is a great choice. It blows away any of the others scopes mentioned in this thread so far. IMO if you can afford the price of the Zeiss, you won't get anything as good, or better unless you take a huge step up in price.

It really just all depends on your budget though. If you only have $100 to spend, those Simmons actually get good reviews from many of the muzzle loading guys.

If you only want to spend $200 or so, I'd look for the Vortex Viper on clearance or a Burris FFII. If you can spend more, go for the Zeiss for sure.