I don't think there's really a "best" in this situation. A sanke coupler is a fairly simple device. It's not like there are options and features to choose from, so I'd go for whatever you can find a deal on. You also might want to consider checking out craigslist for a used one. In fact, I have a few extras laying around that I'd be willing to part with for a reasonable price. PM me if you're interested.