At the end of the day, both will get the job done. But the real story is about integrations and cost.
MemberPress is easier to use and a bit less complicated to set up (because it has fewer options). It has fewer integrations then Wishlist and will cost significantly more per year. Also, keep in mind that the cost of MemberPress doubles after your first year of owning it so you are looking at 3X – 5X the annual cost of Wishlist Member.
Wishlist, on the other hand, has more integrations and capabilities but I feel like it has too many options and could feel overwhelming.
But on the flip side, Wishlist is a lot more affordable, has many more integrations, and also has some more features that you don't get with MemberPress.
For me, I would choose Wishlist because it works with the tools I use and is a much better value.