I had a rover 200 diesel for years using a rack, dead easy to put the bikes on and off (used a bunjee cord to lash the front wheel to the underside), no mucking about having to take the wheels off either (meant I didn't have to remove the kiddie seats as well) so no mucking about with the brakes or accidental pad jamming. On long runs I didn't notice much extra thirst from the engine (from 49mpg to 42mpg on high speeds runs from manchester to holyhead), kept the inside of the car clean and took a minute to get on and off, only downside was that the £30 halfords rack took up a bit of space (9 years old now and being used by a mate) when in the car with it's L shape.
I now have a towbar mounted rack on a focus estate, more of a fiddle to set up compared (2-3 mins) and it holds the bikes a lot lower (2x the bike has been scraped on rough ground) to the ground. It also holds them closer to the rear window so occasionally the wide handlebarred bike "taps" the rear window which sounds awful. It does fold up a lot smaller than the bike rack though. Totally obscurs the numberplate as well.
I prefer the rack of the old car (which are dirt cheap and bombproof btw, 217K miles before it was written off) to the tow bar, but both keep the car clean and mean I don't have to keep removing wheels stacking bikes on top of one another etc. As for security, I never leave my bike unattended so the "security" of having it in the car is of no benefit to me.
edit - also had a escort van, I could stick 3 bikes in on top of each other which was handy but kids meant I had to get a car (the bikes did get scratched). Best I had was a peugeot expert, 3 peeps in the front and 7 bikes in the back all stood up intact, seriously underpowered and drank fuel though.