I've had samples of many different procars. At one time I had a '76 S&S Professional hightop ambulance, bought mostly to be a sister to my '76 S&S Victoria. I'll have to dig out a photo showing both.
Anyway, as neat as the ambulance was with all the lights and things, it didn't quite trip my trigger the way the funeral stuff does, so when a decent offer came though, I let it go.
So my vote would be split between anything limo or funeral related. I have a soft spot for combinations, because of their amazing flexibility and ability to carry 5 people with some degree of comfort. I sold my '54 Series 75 limo a few years back, and still miss it, but I knew it needed a lot of work in order to put it into the condition I wanted. I still look to replace it some day, if anyone has any leads on a '53 - '62 limo with NO DIVIDER.
I love my flower car and hearses equally after that. The photo below was taken in front of Fairlane, Henry Ford's residence. Tom