Mate - seriously that's such a piece of string question.
Its going to depend on how big a batch you are going to boil, type of pot...
I have an old Italian spiral burner that's given over 10years service and still going strong, had a cheap as 4 ring burner that would boil a 205L SS drum.
For mine its more down to having a really good industrial regulator, gives heaps of control and lets you get the most out of the burner.
There isn't a right answer. Depends what you are willing to spend a Mongolian is excellent but so are lots of other options. I don't even know what a Gas One or Dark Star are probably as I haven't been in the market for a burner for a decade or more.
Mark