I have all the muzzleloaders mentioned above, I believe.. The Triumph is a shooter however I do not care for the stock, maybe the Triumph Bone Collector feels better?
TC Encore Pro Hunter: Bought two frames and barrels seperately, one .50 Bergara Encore barrel, one .50 Bergara Encore barrel and a .45 Encore barrel. The Bergara's in my book are top notch barrels that just take minor tweeking. The Pro Hunters have a very heavy trigger where the standard Encores I have shot have very nice triggers. For the Pro Hunters its an easy trigger fix with a Bellm #3 spring and you have a nice 2.75-3lb pull. The Pro Hunters are also nice because you have the option to buy a rifle, shotgun or rimfire barrel.
One muzzleloader that was not mentioned that I feel needs mentioned is the TC Omega. I have the .45 and did have the .50, both with laminated thumbhole stocks. They both are/were excellent shooters and very easy to clean. I handled the Omega Dream Season and it shouldered great, never shot one though.
I have/had Knights which required Lehigh plugs for ignition with Blackhorn 209 but are/were great shooters. The Mountaineer comes with a Lehigh plug already and Grouses groups show it's a great shooter.
Here is the best thing I can tell you to do.............hit Bass Pro or Cabelas and handle a few. See which one you like the best, fits you best and is in your price range. They will not have the Mountaineer though.
After handling a few and narrowing it down check the classifieds on the various forums. Great deals can be found from time to time.