Used a trunk mount rack the first year. It was a pain because I started on a heavy Walmart bike. A pain because the bike didn't fit well (full suspension.) A pain because it marks up your car. A pain because I ride every day after work so the bike sat there rain or shine.

Now with my much lighter Giant Escape I put the seats down in my Jetta and take the front wheel off. My bike was locked in the car out of the elements every day from May through November sheltered from the rain.