I started with a Thetford model 165, then bought their smallest, the 335 model.
It didn't take long to realize that I particularly disliked emptying and cleaning out the holding tanks!
Carrying the heavy unit with either the fresh water or holding tanks full wasn't much fun either!
I then discovered the BranQ Portable Toilet, a 22 litre, immensely strong and light square plastic bucket with fitted toilet seat and lid.
Tesco 22 litre waste bin bags fit perfectly and make for horror free, hygienic disposal of the double bagged waste.
A 3 litre Comfort laundry liquid bottle takes care of pee as I keep the 22 litre toilet for solid waste only.
I have now replaced the BranQ 22 litre Portable Toilet with the BranQ BBQ Bucket, which is exactly the same injection moulding as their 22 litre toilet (in a different colour) but which has a very strong lid designed as a seat (with a rating far beyond what I weigh).
I keep the toilet seat and lid from the original 22 litre toilet to replace the standard seat lid fitted to the BBQ Bucket for when I want to use the toilet.
This gives greater practicality as the BBQ Bucket has the 22 litre bin bags fitted, ready to use, and inside that I keep a bag of smokeless charcoal briquettes and dry wood.
So, I get to use it as a seat when required, and in that role it also stores my charcoal briquettes, dry wood and fire kit, and to use as a toilet, I just swap the lid for the toilet seat and lift out the bag containing my briquettes and dry wood and its ready to use.
There is a world of difference between emptying and cleaning the 3 litre pee bottle and disposing of the double bagged toilet waste and cleaning the toilet and seat/lid (even though no waste matter came into contact with anything other than the inside of the bags fitted into the toilet bucket) than the horrors of emptying the heavy Thetford holding tanks over a toilet bowl!
This is such a personal preference that there is no single right way, only what one finds to be the least awful...
Edited for typos!