There's all kinds of bike racks, but I think hitch mounted racks are the most versatile because you can put it on any car, truck, van, or suv as long as you put a cheap Walmart or Auto Zone hitch on the rear of the vehicle. The hitch type will enable you to have just one rack for all your vehicles instead of two or three.
There are plenty of hitch styles out on the market, the one I got is called the Bonelocker, this is the most secured bike rack made so if your worried about someone stealing your bike while your eating this hitch would help. And the rack is very strong I can go on and on but just read about it here instead:
Bonelocker: Premium Hitch Mounted Bike Carrier for your Truck, SUV, or Car Made in the USA
If you can work on bikes then you can install your own hitch, it doesn't require welding, just about 2 hours of time at the most. For smaller cars it's probably best to lift the back end up with jack stands or ramps (block the front tires) so you have room to craw under and work. Get the cheapest hitch because you won't be hauling more then 75 pounds and the cheapest hitch is rated for 3,500. And you'll need a hitch pin lock, the carrier itself comes with a lock for locking the rack and bicycles.
But a lot of those car racks for the rear end up scratching the paint and some will only fit specific cars like only hatch backs or only trunks; roof mounted jobs see bikes getting wiped out by garages, trees, low overhangs, drive-thru hanging bar, etc.