If you do not need the macro, I consistently hear that the panasonic 12-32 is better optically than the 12-50, especially at the wide end. Also, if you do not need the macro, the Panasonic Lumix G Vario 14-42 II model is supposed to be the "best" of the 14-42 zooms by Oly and Panasonic. Panasonic has also recently introduced a 12-60 that might work. Jury is out still on how it compares optically.
That said, I am not always sure that minor differences in sharpness can easily be detected when you consider that underwater photography usually means we are moving while taking pictures of moving subjects through water that is not really as clear as we often describe it. Comparing underwater to above water photography, it would be like putting a clear filter of uncertain optical qualities in front of our lens (the port) and then taking a picture through a window (sea water) that may not be really clean.
If you need the macro and the wide end in one lens, then the 12-50 is about the best you can do.