There used to be only 2 types of racks. Roofs racks and hang-n-bang. People that loved their bikes (and were not stupid enough to drive into the garage with them on the car) got roof racks that securely held the bikes so they would not bang into each other and they usually only touched contact points like dropouts or wheels that wouldn't dent or damage the frame.

Everyone else hung all their bikes together on a horizontal bar on the trunk and let them bang against each other for the trip. Over time, padding on trunk racks got better, but bikes still contact each other and can get dented and tires can get ruined by being in front of the exhaust pipe.

Hitch mount racks started as hangers, but now they have some very nice ones that hold bikes individually in trays by the tires or with well padded arms.

So...

Roof rack or new tray type hitch mount with separation if you don't like your bikes to bang together. Both are very secure.
Roof rack if your car is short, you're tall and you don't mind lifting bikes onto the roof
Hitch mount if car is tall or you don't want to lift bikes.
Roof rack if you're smart enough not to drive under low stuff. I'll admit this takes a certain type of paranoia. I have had roof racks for 30 years so I don't even go under low trees *without* bikes on my car!!
Rear mounts if you don't mind bikes getting smashed if you're rear ended by another car. At least it will probably be their fault and they'll have to buy you new bikes.