As is usually a very wise thing to do, I'm gonna go with Gene Greco here.
Winged Foot might have the best two-course combination in the USA in terms of architecture and test of golf, but I have zero doubt I'd have more long-term fun at MPCC, as seaside golf is pretty much always gonna be better than parkland for me. I believe I'd get all the test I'd ever need at MPCC, also.
For a very basic reason I believe I'd take Ballybunion over Portrush, btw: the former has always been very welcoming and one feels like a member for a day; at the latter there are a lot of rules and forbidden places and one feels tolerated more than welcomed. I believe I'd fit in a lot better at Ballybunion. I'm among the sick puppies who likes the Cashen, also.
TH