In reply to kipper12:
Gas stove: cheaper to buy initially, clean and easy to light in good conditions, the simple ones are very light.
Petrol/multifuel: more expensive initially, but fuel is much, much cheaper my omnifuel will do 2/3 medium sized gas canisters (~£8-9) worth of cooking on less than half a litre of petrol (~50p). Obviously, it doesn't take long for this to add up and save you money - mine has paid for the initial outlay already. They cook much better at altitude/in the cold - I find almost no difference running mine at -5C or 25C. They might usually be a touch heavier than gas ones (the stove, that is), but overall the difference might be smaller than you think. If I was going out for 3 or 4 days, and I still had a gas canister from my last trip, then I'd take that and one (or maybe more) extra gas canisters with me. With the petrol stove, it doesn't matter how much fuel there is left in the bottle from last time, I just top it up, and take that - no need for extra canisters or bottles. They do require a a little bit more practise, require a bit of cleaning, and can be less pleasant in enclosed spaces.
If you've got the money of course, you could get an omnifuel, and then you can use both
Tim