I bought the full size Transit about 2 years ago (medium height/medium length) and really like it.  I moved up from a Chevy Astro and couldn't imagine going back to a smaller vehicle.

When I drove the Astro I had to shift products and tools in and out of the van every day based on the job and ended up strapping long stuff like conduit, shades, etc. on the top which was time consuming to load and unload.

Now with the Transit I keep almost every tool in the van, plus lots of parts/supplies and even have room for lots of demo stuff (lutron lighting & shades, acoustic stuff, etc.).  The cargo area is over 10ft long the longest shades, conduit, unistrut or whatever just goes in the back and I haven't installed a TV yet that didn't fit easily in the back.  I do custom work including woodwork, metal work, acoustics, etc. so keep a compressor and pneumatic tools with me all the time.  The only tools I don't keep in the van full time are table saw and miter saw.

It's got the 3.5 Eco Boost engine (twin turbo) and I average 14MPG fully loaded with ladders on the top.  Highway MPG is around 17MPG and in town with hills is about 13MPG.  I only drive 6000-8000 miles per year so not really concerned about fuel economy and the convenience of having everything in the van far outweighs the economy of a smaller vehicle for me.