This will be the tightest comparison of membership plugins because they are both really close in features, ease of use, and solid backing.
If I was to give an edge to one, it would be MemberPress if you need to have an affiliate program because it’s included in their $349 plan.
If you have your own affiliate management plugin or if you already use AffiliateWP (the market leader), then I would go with Restrict Content Pro because it’s more actively being developed, looks much better out of the box, and has a lifetime payment option available. Oh and you can install it on unlimited websites.
One big negative for me with MemberPress is their fake 50% offer if you buy in 4 hours. Don’t fall for shady fake scarcity tactics like that.