In reply to Removed User:
MSR are the Volvo of stoves, all others pale in one way or another. Which leaves choosing the right model. For efficiency, lightweight trips with no actual cooking involved (think winter/high altitude water melting, boil-in-bag meals etc..) the MSR Reactor is unbeatable. These stoves are self-contained units including pot and are very fuel and weight efficient, but they're not field maintainable.
For high output, versatility and actual cooking the MSR XKG is the long reigning champ. The WhisperLite models are also right up there. The biggest advantage of the white gas (naphtha) burning stoves is their field maintainability - at 6000m you should bring a maintenance kit (MSR have a couple of options) and have practiced trouble-shooting & fixing the typical issues: clearing a clogged jet, lubing or replacing a pump cup, identifying potential leak points and replacement washers and where they go. Once you know these basics, keeping them running well becomes second nature. Strip one down a couple of times and you'll get the hang of it quickly.
I'll second the caution about contaminated liquid fuel, always run a stove check on a new fuel supply when travelling and if you experience poor performance double-check the fuel bottle and look for a distinct water bubble in the bottom of the bottle. Decant and ideally filter suspect fuel. In winter and high altitude I always run the stove before departure.
Post edited at 16:50