Have used all combinations over the years
Inside car - never quite enough room, muddy bikes just a nightmare, security still a worry as they could just smash window (oh for a car with a decent steel loop in the boot to lock things to)
Tail rack - PITA with 'odd' shaped bikes, PITA getting into the boot for stuff, PITA putting it on and off and never feeling 100% confident it would not launch off the back on the motorway, zero rating for security!
Tow bar rack was great, really wonderful for pulling up at garage jet wash with two muddy bikes on the back and blasting them clean. Biggest drawback was that I always worried about getting rear ended, pain to store and a pain to get into the boot, or use the boot as a seating/getting changed area - security big worry on some cars, but another car I had had a nice big loop in the tow bar that allowed me to put a chain through frame and rack, so depends on the car.
Of all of them, the Thule roof rack was best as it allowed me to sit in the boot when getting changed, quick and easy to use, never felt like I was going to lose the bike at speed, and lock would go round the frame and roof bars (car had proper bars not gutters)