Using a tow dolly, you should tow rear wheels up. If you tow all 4 down, then be sure to do the bungie cord trick for the steering wheel so it doesn't get out of hand.
I decided to go with a motorcycle trailer, MC2F from Aluma. Got one used for less than a tow dolly. Tried loading as a tilt trailer, which is possible, but too scary for me, so I ordered a second ramp and use two jacks to support the back end fold-down portion when loading unloading. Works very smoothly and just fits my 2015 Smart ED.
I did make some additional mods to extend the aluminum channel at the rear to support the fold-down end better, since the wheels overhang on to it somewhat. I'm also now adding electric brakes to help my RV braking and safer downhill travel.
I back it on to get at least 10% tongue weight. The red mark in this picture marks the center of gravity. Couldn't find a better picture at the moment.
Good luck.