I have the medium height, medium length transit and think it's the perfect size for me.  I have the Prime Design ladder rack on top, so it's about the same overall height as the high roof van.

I considered the high roof van to be able to keep all my ladders inside, but the med roof with ladder rack on top allows me to carry longer ladders.  I usually keep a 3ft or 4ft ladder inside and then have a 6ft and 10ft on top, but can swap the 10ft for a 12ft A frame or extension ladder without adjusting anything on the rack.

The roof rack also allows me to strap long shades and other materials on top that won't fit inside.  I have about 10ft 8in length available inside the cargo area behind the partition, but have put 12'-16' shades on top and even some 20' PVC.  With a high roof van and no roof rack, I'm not sure what you'd do if you had something that's too long to fit in the back.

I like the medium length too.  Even with this it's difficult to find parking sometimes, but usually not too big of an issue.  With the longer van, it would be a lot harder to find parking that it fits into.

I'm able to carry everything I need including a small compressor and some pneumatic tools, folding table & chair.  The only tools that I use occasionally and don't carry in the van all the time are a chop saw and table saw.