I don't have a rack for my second-gen Prius, but I've seen all kinds of racks on them.

Hitch mount is probably the easiest for removal/installation - you definitely want to be able to take the rack off and on easily, because even without bikes loaded it will really eat into your gas mileage. Some racks flip down so you can open the hatch without removing them. But then you have the expense of installing a receiver that you won't be able to use for anything else.

Trunk mount is least expensive and I've seen a number of Saris Bones and similar racks. But they're a hassle to install and remove, potentially scratch the finish, and you can't get to the hatch while they're on.

Even rooftop racks might interfere with your ability to open the hatch, just because the roof area of a Prius is so short. I've seen people with roof racks with really long rails.

How many bikes might you be transporting, and how particular are you about how they're carried? One bike fits easily in the trunk area. Two can be stacked with a blanket between them and IMO they're just as safe that way as they are outside the car, exposed to rocks and debris thrown from your wheels or other vehicles.