This is an interesting question.
If you are "sure" about the LT direction of the trade, then a short TMF position will pay the most.
I do not like triple leveraged mainly for psychological reasons: I am wrong more often than I would be happy to be and hence triple positions put you under great stress when you are wrong. It basically deprives me of "time to think" and I feel pushed to take a decision to cut losses. A double ETF make my life easier.
The real question is about the trade direction: a short Treasury's is by essence what the whole market is thinking about and has been thinking about since QE started. However, in my opinion, the trade does not have legs as there is still a big Treasury's buyer in town.
A short Treasury's trade is very similar to a long gold trade. The first bets that there will be panic selling in Treasury's that will overwhelm the Fed. This will not happen! The second bets that there will be markets instability due to a rise in interest rates and a search for a new safe haven that is cheaper than Treasury's. This is a more probable trade.
Regarding interest rates, I prefer to trade the housing market, because it is linked to rates, but also because there is no buyer of last resort that puts a floor under that market.
For example: SRS gained 5% yesterday, while TBT was down.
I believe that the SRS long trade is "done" for now. I liquidated the position yesterday and will buy on a further pull-back probably after the next Month QE program has been published.
I think that TBT is a short term trade now while SRS could be a long-term opportunity after the VNQ bounce has failed (which is not the case yet.)