I would highly recommend the Thetford Curve.
Ours, conveniently located across from the fridge at the back of the van, has worked out very well on our trips.
This particular model has the advantages that...
1) it's home toilet height, no need for a step under it
2) it's electric fill... fancy! You fill with a pushbutton, flush with a lever on the side.
3) for an additional $20 or so you can get a baseplate that attaches to the floor and the toilet clips in place... easy to undo to take apart and dump, but very solid when clipped in. ON ours, I made an L bracket bolted to the wheel well because I didn't want to make holes in the floor!
4) built in toilet paper holder on the side
The clean water tank top is a bit loose, but as long as you don't fill the tank to the top, it won't spill any water (ask me how I know!)
We use Coleman deodorant because the Thetford stuff that came with it smelled like a dirty gas station mens room.... the Coleman stuff smells nicer out of the bottle and we have never smelled the toilet on our trips, even when the van got to 100 degrees plus in a few parking lots.