i would get the cradle style.
i have a hitch cargo rack and a buddy who welds. i am going to ask him to fab up something out of any scrap metal that he has so i can attach it to my cargo rack and then strap my bike to it. i figure two metal braces to hold the front tire in place and a few quick fist clamps should do the trick. something similar to what hophead posted.
I just made a hitch mount bike rack copying (to the best of my ability) the Yakima design that Xela posted here on page 2.
It's an absolutely ingenious design. It captures the front wheel, holding the bike, and the rear wheel holder is positioned to kind of pull the front wheel back into the cradle.
It's so easy to load. Yakima advertizes "loads in 10 seconds". Just pick up the bike and drop it in. The one I saw had a little strap around the rear wheel to keep it from popping out if you go over a bump.
I particularly like that the only part of the bike that touches the carrier is the tires, so there's no rubbing or scraping the paint.
The one I built came out specific to our bicycles. One with 26" wheels, the other 28" wheels. It's a dual carrier and the bikes can't interchange. I'm sure Yakima's is adjustable or designed better for multiple bike sizes.
Building mine I found out that the hold points on the front wheel have to be pretty high to be effective. And the single hold point on the rear wheel has to be high enough to pull the bike back putting pressure on the front wheel. But not so high it hits the bike frame.
Your carrier will probably come out spcific to your bike too. By the time you take into account the wheel size, wheelbase and tire size, pretty much only the one bike is going to fit. (my experience)
I built mine out of 1/2" pipe and 5/16" steel rod. (junk I had on hand). the only out of pocket cost was $7 for a can of hammer finish paint from Lowe's.
Good luck with your project.