In reply to James Malloch:
Anything over L1 doesn't fit neatly into a standard supermarket car park space, so once you go beyond that is kind of a step change with regards to parking in carparks.
For on street parking, obviously the longer the van, the more likely you are to have to carry on past a space.
A longer van doesn't necessarily change the fuel consumption much - although if the extra space means you end up carrying more weight then it will to an extent.
It's always a balance between comfort and ease of use, and only you can figure out where you sit on that. On long trips abroad the extra living space of an L3 is a big bonus.
OTOH, an L1 might successfully take you up a rough spanish crag access track that the L3 could belly out on. I had an L1, and fitted heavy duty rear springs that lifted the back quite a bit - was very reassuring when driving like you were in a catelonian rally stage to keep momentum up the hill.
The L3 requires a more circumspect approach so you want a good pulling engine. The 2.2l engine in my L3 relay pulls really well.
I'd say think about what you're going to use it for the most, and choose based on that, compromise on the things you're using it less for.
One thing I would recommend is, whatever length you go for, if you're using it for long trips make sure you can stand up straight in it. My L1 was an H1... never again.
Also, if you're not sure, it's much easier to go from a smaller van to a bigger van than the other way round IMO... You get used to the comfort 🙂