3700 is a two handed. The 920 JLC was an ultra thin movement with an interesting rotor. The PP 240 is ultra thin with a special rotor. It is Patek's reply to a thin automatic and hence more coherent with the original and with the concept of the watch.
I feel the 324 is a very efficient, well constructed and probably cost effective movement. But it is perhaps also a bit more generic in its design.