Best caravan toilets

The OP asked "what's the most important thing to consider when purchasing a first van".  I would say the toilet falls way down the list and almost every modern van has a built in cassette toilet of some sort, so you won't need a porta potty type or separately purchase a toilet at all.

Go and have a look at some caravans at a dealer and the layout and size (so you can safely tow it and it can sleep the nuber of people you need) are the most important things, whatever else is/isn't inside it is 'window dressing' really.