I would recommend the Thule T2 bike hitch mount rack. It will do everything you are looking for in a bike rack.

I have alway been a fan of roof mounted racks. I have a Thule Fork mount system with the separate wheel holder. I have never been disappointed, except for the time I ran into a car port. The problem I have with the hitch mount systems is that most of them secure the bike to the rack with the top tube and given the funky angles and designs there are now day with the frames the bike always sits at a weird angle. The other two issues I have with hitch mounts is that the are tough to lock your bike too and if you are carrying more than one bike at a time your always seem to get some damage because you forgot to protect an area from rubbing against the other bikes. Just my .02.

anything BUT roof mounted racks...

+1 for the Thule T2. Stable, ease of use, and it's touchpoints on the bike ensure zero rubbing and knocking.

+2 Thule.

I have a Subaru and bought a Thule roof rack....I am switching to a hitch mount! I hate after my rides, I can't go to Whole Foods because it won't clear their parking garage! But I will say this, other than the inconvenience of garages, my roof rack has been great but I also don't carry my bike up there for long distances for fear of losing something, I always put it in my car. If I had a hitch mounted rack, I would feel more inclined to use it for long distances.

I have a hitch thule and really like it.
I heard some story of people forgetting the about the bikes on the roof and pulling into a garage....
i have a garage and i would be sure to forget at some point about the bike on top.

what's your ground clearance like on the WRX?
isn't it going to be worse with a hitch mount?

I've got this rack for my subaru legacy:
http://www.thuleracks.com/product.asp?dept_id=8&sku=910

and it works really well. I've been using it for about 3 years for both mtn and road bikes, and have never had a problem.

I have had a yak rack for 15yrs now... Roof mount, I love it. The thing that worries me about rear mount is a rear end collision. I have never forgotten about my bike(s) being on the roof. I do have a buddy that did, it wasn't pretty (he cried a lot)

The Saris thelma rack is fantastic. It's solid and easy to use and won't allow your bikes to touch each other since they are held by the wheels. The design doesn't have any part of the frame touching the rack. I have the 3 bike version and love it.