I've tried short term car rental services where you can rent a car for a few hours. Half the time it worked well, the other half of the time it was a hassle.

Some problems I had were that sometimes the car wasn't where it was supposed to be, a couple of times the car was double booked, and quite often the cars had other people's rubbish in them. One time the car was full of sand (clearly someone had been to the beach).

I think in my case I'd always prefer to have my own car.