We went through the same process.
Our requirements were for:
4 seats with 3 point belts, 4 berths, to accomodate myself, wife and 2 children aged 4 and 3, with ability to use it as an everyday vehicle. It also needed to be able to double as a tow vehicle for our boat. If it was side conversion we wanted a walkthrough to the cab since we did not want the children getting out on the road side when abroad. It also needed a decent size boot, ideally with sliding rear seat along with the ability to fit under height barriers in car parks- pretty much every carpark around us has height barriers
We looked at the Merceedes Vito, Mazda Bongo, Ford Transit and vw t4.
The bongo seemed a bit too small and whilst seemingly reliable and nice to drive may have overheating issues, the engine seemed overly complicated/ sophisticated with a complicated cooling system, four wheel drive and reliance on electrical systems, even the roof on some opened via electrics. The vast majority came in automatic only- not so good for towing or fuel economy.
The merceedes frightned us with rust issues and seized injectors, we have always worked on the simplicity principle and I like the idea of doing some maintenance myself. The vito engine seemed more difficult to work on/ access than some. We also were unable to find much information on their towing ability .The conversions we looked at seemed smaller than others, not sure why as a tape measure showed comparatively small differences, but they just did not feel right.
My wife vetoed the transit on bais was too "white van", we also found there were few converted ones around to either buy, or view for ideas for our own conversion
Having discounted the above we ended up with a vw t4 by default, initially I was dubious believing VW to be hyped up as "fashionable". Having now lived with ours for a year I have to say we made the right choice- the driving position feels right and it does not feel too big for everyday use and is not too bad fuelwise despite being a 2.4 engine and having the aerodynamic qualities of a brick. Ours has sliding rear seats to give an enormous boot if needed and the walkthrough cab is great with young children.At less than 2m high height barriers are also not an issue Our only grumbles are that it is not the quickest in the world and is noiser than some more modern vans at speed, but as we tend to avoid motorways we can live with these points.
(Ironically we have just bought a dandy trailer tent to go with the van, but that is beause two wet weeks in June with the four of us in the van, with awning tested our sanity!)
Good luck in whatever you choose