I did a massive amount of reading up on this very subject approx. 10 years ago and came to the conclusion that if I was converting a van with a rust resistant fully galvanised body shell which was in either new or good condition, then the insulation with the highest level of thermal insulation was/is closed cell spray foam.
I also looked into doing it myself - V - professional and came to the conclusion that there was very little difference in the costs, so I then started looking into which company would appear to be the most professional, and this is where I made a distinct mistake choosing a company that had been widely used by members of the SBMCC.
Although my installation has proven to be very thermally efficient, I discovered that if the operative pays exceptionally close watch on the heat of the solvents then they should be able to achieve a virtually smooth finish, instead the man I chose didn't even check the temperatures once and the result was exceptionally messy and required an enormous amount of cutting back. And this is exactly what other people had experienced.
Since that time I have met a company who were so exceptionally methodical that their finished results are almost mirror smooth !
I won't give the names of the companies as I honestly do believe that it would be wrong of me to do so, however, do a lot of research and I can assure you that you will not be disappointed.
Phil