You get full credit on cheapo United fares with KF, that's why I'm with them currently. I looked at TK but most of the fares I'd be flying on would be 0% earning to TK. So while yes the 2 year thing is really attractive, it all depends on what fares you're buying. If you are buying J then pick whatever, if you're getting flexible econ, then I'd look hard at TK. If you're flying cheap for leisure like me, TK isn't really relevant unfortunately.