Towbar racks are very good indeed, particularly if you're going to be carrying several bikes. they're very stable, good for fuel economy, easy to load and you can keep an eye on the bikes while driving.
Try to get a wheel support rack, where the bike stands on the rack rather than hanging off poles higher up. Better for the bikes, less contact between them. Ours are secured on each wheel and on one crank – very stable and secure yet car and bike paint are untouched.
Some towbar racks fold up for storage – some of the Thules – but quite expensive.
Pendles are very heavy and stable all steel tubing, no aluminium, no plastic) but don't fold up.
Roobox.co.uk have a good looking fold-up wheel support rack for about £180. Can't remember the make, no-one famous, but looks great.