I recently got a set of Rhino Ramps. I got the heavier set, rated at 6K lbs each, or 12K total.

They are quite wide enough for the (stock) tires on my W210. They have a rubber bumper at the bottom of the toe to prevent sliding, and that feature seems to work fine. I wedge them under the front tires, align them so they're straight, and drive right on. They have never slipped.

I don't know if there are better options, but I can recommend them.