On the wagon, I've found a hitch mount is the way to go. Hitches are cheap and easy to install (I paid $40 plus off/on labour, about 45min each) or they are $170 New from Sub Cal plus probably and hour labour if you want to pay someone for 7 bolts.
I picked up a platform Swagman from JC and it works great. I can open the hatch (07) with a bike on the aft position. We did lose a bike last weekend due to me taking a u-turn too fast, the bike skipped out of the tire holders and the angled top-tube allowed it to pop out from under the hood. Was only doing 40km/h and the only damage was to the nose of the saddle. We now run ratchet straps from the chain stays on the reciever, up around steer tube/seat post back to the other chain stay. It flops around a bit but as long as you drive like you have four thousand dollars worth of bike hanging off the back of your car, you should be fine.