Both are excellent frames of course. The Burner is probably a tad more on the neutral side on handling and the RX-100 might be a wee bit quicker. RX is a bit lighter too. Depends on your tastes as these are very compareable frames though. Personally, I like the lower leverage ratio on the RX and the fact that it's manufactured by Titus themselves but I'm slightly biased. This is all nit picking but that's what we do around here. Sizing is a bit different so I think that should influence your decision MUCH more than anything else.
Other random thoughts...You also can't ignore the Burner is a killer deal right now. Burners are ready to ship but it might be as high as a 2-3 month wait on the RX depending on what's in stock, what size color you order and where they are in the production cycle. Just to throw another wrench in the works, rumor has it Turner is supposed to have a new replacement frame out this fall. 4" and lighter than the Burner.