The highest value redemption now is Singapore Suites for sure. But with them being transfer partners with TYP, SPG and MR, I'd rather use my UR for Hyatt, after the United deval last year. UR are the only way u can get Hyatt points without actual stays. You can still get United points through their CC. Since the Hyatt card gives night credits instead of points, again, UR is the only way to get Hyatt points. Anywhere. And since The best Hyatt properties cost the least of any chain, they're the best deal for hotel points anywhere. Even lower category Hyatts get good value. Next week I'm staying at the Hyatt place LGA. Over $400 a night, but only 12K hyatt points. 3.5 cpp value.
Southwest has a fixed value for their points under 2 cpp. BA has terrible YQ, and on short hauls I'd rather transfer in my Canadian MR, which is the best value north of the 49th. Korean is...complicated. So for me it's Hyatt.