I'm not sure if the NZ anomaly you refer (0.7 MEL-SIN to get 1 econ MEL-NZ) takes into account the upcoming reduction in airbucks earning rate to asia?

If flying mainly paid business I'd consider BMI (need european address) or Miles and More. While awards cost more than Kris Flyer, the earning is 200% vs 125/150% (on SQ metal crediting to Kris Flyer) and only need to earn status every second year. For me it would depend on how much non-SQ business flying you may do, since 150% on SQ flights to KF is probably better than 200% to M&M, but 125% is probably worse. (There are other factors like the award zones are different with KF having more of them than M&M - can be plus or minus depending where you want to redeem.)

For UA Mileage Plus the main considerations are how much you'll fly them, and can you take advantage of their cheaper & more flexible awards (bearing in mind availability using MP awards on other airlines is reported to be worse than other *A FFPs).

I think we're in similar situations. I credit some to KF for the upgrades and certain cheap awards but tend to credit more to other programs offering better earn/burn rates. As long as you fly enough on SQ to maintain PPS status you don't need to worry about whether or not make *G on another FFP.