Both are great choices and really you can't go wrong with either one. Northstar has a very slight efficiency edge but the Whisperflow can handle a bit more suction loss without cavitation. Whisperflow is also easier to find as two speed version.

Also, if it is a new pool, you might want to stick with all the same equipment since you can get a free extended warranty that way. Otherwise, you might want to go with the best price.