In reply to Tom Green:
Gas suffers in the cold, as it relies on the vapour pressure of the gas in the canister which is temperature dependent. Having said that, they are light and effective if you can warm the canister a bit before use. In a sock or hat in the sleeping bag works.
Jetboil type stuff is great for boiling water. If you plan on living on soup, boil in bag or dehydrated stuff they are great. Probably the best lightweight option for taking on a route. Crap for actual cooking though.
For options with separate pans:
Gas stoves that screw on top of the canister are light but crap if there is any wind.
Gas stoves with a hose and separate burner work better but weigh more. If the hose is long enough you can be naughty and get a boost by dipping the canister in the warm water. Primus gravity is a good option.
Then there's petrol. No problems with pressure but faffy and tend to flare. I have turned away from the fancy multifuel stoves lately and gone for a v simple optimus 123r with midi pump. The pump bit is vital as it's crap in self pressurising mode.
MSR XGK and Whisperlight international or something like a primus omnifuel would be more mainstream options.
tl;dr: If I had the budget for two stoves I would probably take a jetboil for the routes and something like a primus gravity for the valley.