Yes. One with which you earn other ways.

Even with an airline program that gives more miles than average for a 2-day rental (BA gives 500, and Southwest gives 0.5 credits), if you only do that oocasionally and don't earn the same miles with anyone else, then you're not likely to ever get to an award level. So what's the point?

So I can't give you a good suggestion until you explain which arilne program(s) and/or hotel program(s) you already collect with (presumably in ways other than rentals). I presume you a renting because you're flying (or taking the train) to somewhere, and once you get there, if you're renting for 2 days, you most likely need a hotel stay, so I presume you collect with someone, but I have no idea who.