For me this is the problem with several polls of late, missing out the obvious options. Gas trangia stoves are very efficient and gives the best of both worlds. So, if you answer Trangia, or gas, what do you really mean? What does the result mean?
But if you are using a gas conversion, then surely you are using gas?
Is the trangia a windshield, or a stove?
The question is "gas or trangia?" ...which implies gas stove or trangia burner, since it's silly to compare a fuel type with a windshield. Perhaps it should ask "gas or meths?" to be more accurate.
Anyway, back to the argument...
A few weeks ago, I bought a jetboil and for what it does, it's awseome. Talk about fuel efficient. It will bring 250 mls of water to a bouncing boil in 90 seconds flat. So what I hear you say? well that means an awful lot of boils out of a single, tiny 100g cartrige of gas. You have to carry a litre of meths to get the same from a trangia - and a litre of meths weighs a kilogram. The jetboil is fast, convenient, thrifty and easy to use. For cleanliness and fuel efficiency, it knocks spots of the trangia.
But... the point is it's not perfect for every situation. For cold weather, altitude, power output, boiling snow and access to fuel, you cant beat a petrol stove. But that doesnt mean you should take one on every trip.
Sometimes a trangia may be preferable than either gas or petrol. It depends on what you are doing, what you need from the stove, where you are going, for how long, at what altitude etc.
I dont think it's possible to simply answer gas, meths or petrol to a "which is best?" question.
The stove which lives in the back of me landy is the jetboil - the convenience of it is impossible to ignore. I can add 250mls of water to it, light it with the pietzo ignition, set it on the wheel arch and by the time I've added coffee to the cup, the water is boiled. The stove has cooled and can be packed away long before I've finished me cuppa. It's the nearest thing to having an electric kettle that I've found. Because the stove connects to the pot with a bayonet mount and because the pot is insulated, you can even hold it in your hand while it boils.