First off, let me just say that if you have the cash to plop down on a fully equipped Z520, my hat's off to you
That said, my opinion is this:
Go and climb over, under, around, and through every single one of those boats you mentioned. Next, take every one of them for a test run, preferably with at least some chop on the water. Look at the interior layout, storage bins, the works. Pay close attention to the items that are most important to YOU. You'll find one that suits you more than the others. Buy it. Of the three you mentioned, I would lean towards the BassCat. I would also take a gander at the Skeeter I-Class boats, Champion, and Legend.
For engines, I've had good service from Johnson/Evinrude for over 20 years and see no reason to change. It would be the E-TEC for me.