The #1 issue with propane cookers is that the BTU ratings aren't always accurate. I talked with a heating engineer once about this. Apparently, there are no solid industry standards when rating propane cookers. A BTU is a BTU true, but the way you measure it can take different forms. So when looking at burners you can't really compare between manufactures. What may be one companies 50K BTU is anothers 30K BTU, and you'll get the same performance out of each. BUt you may spend more to get the 50K thinking you are getting more power.
The good news is that you CAN make comparisons within a manufacturer. So if you look at one manufacture who has a 50K, 100K and 150K burner. You can feel confident that they are each more pwerfull than the one below it. Because the company uses the same test method for all its burners.
In general, I'd suggest looking for burners that are 1) used by many brewers and 2) look for ones that have 50K or better BTU ratings.
I use a bayou classic and I am pretty please with it. I also have a canjun cooker that works just a little bit better. I find that the bayou 'banjo' style puts out a lot of heat, but the air intake could work a little better at high out put. The canjun style seems to work great at all ranges of output, albeit a little less powerful than the bayou.