I have all three types of rack in my arsenal, and they all have their advantages.
All of my cars have been wagons, H-backs or SUV, and the current bike fleet includes road, MTB, a 16" kids' bike and an adaptive 3-wheeler, so I have to be versatile

Strap-on trunk rack: Pros: Most cost-effective, easy to load, no permanent attachment to vehicle.
Cons: least secure (lockability) restricts access to trunk.
Best for Occasional use.

Hitch Rack: Best loading access, 'Wheel tray' types work best with different size bikes on the same rack. Integrated locking options. Easiest install-removal from vehicle (after initial installation) easily swapped between vehicles.
Cons: Requires receiver hitch, adds to vehicle footprint, even when empty. Fold-away and quick release options add to weight and cost.

Roof Rack: Most Secure, allows full access to vehicle when loaded, modular: can also carry skis, kayaks, cargo, ect.
Cons; Most expensive, semi-permanent mounting. (also sucks to load on high-roof SUV's)
best long-distance hauling