We had a cheap, hang-on carrier, used it a few times for 2 bikes. It was supposed to take 3 but broke the first time we tried that!
As we use it fairly often (and my bike is heavy) we got a towbar fitted and bought a 'ride on' carrier. This is better for me as my back problem makes lifting the bike high difficult - but it is less easy to secure the bike single handed. We got a 'Thule' carrier for a very good price from a shop we found via
Ebay.
If your car is high it might make getting the bike onto a roof carrier difficult and you will have to be careful of places with height restrictions.
It's horses for courses really, you need to decide how often you will use it, for how many bikes and what your physical capability is before you make a decision.