First of all, you should keep in mind, camper toilets would have some pros and cons because these are not your fast flushing home toilets like this. However, here, I am sharing the best options with you.
Natures Head Composting Toilet - Though it is an expensive toilet but could be a great option for eco loving campers. See its image below:
Dometic 970 - I personally like it because it is quite easy to use and give you a luxury camper life feel.
You can see more options here.