I would recommend one that goes all the way around the seat. I received one as a gift that only covers the back and the front of the seat, and the first time I used it my son immediately leaned over to taste the (uncovered) side of the cart.
There are some that fit both shopping carts and restaurant high chairs. That would be nice, too. Sigh.
There are some that fit both shopping carts and restaurant high chairs. That would be nice, too. Sigh.