Supposedly the higher humidity in commercial fridges are explained because they are opened and closed so much, that's creating the humidity. But I don't know, I find some coolers are just more humid then others not matter how used they are or not.
Personally, I've never figured out which brand has the least (I've worked in many, many professional kitchens)..........it's like jeans: each one varies a little bit even though it's the same size.
Professional kitchens often choose coolers based on how easy they are to clean/maintain. A cooler with the motor on the bottom is easier to vacuum and keep the motor clean then a cooler with the motor on top.
The tips that I CAN help you with when shopping is really looking closely at the sizes. There are commercial coolers that aren't deep enough to hold a sheet pan. Which means getting a full sheet cake into it is a horrible experience, you have to twist it to insert into a cooler. I've also run into coolers where the door opening isn't wide enough for my larger wedding cakes to fit in to. Like a 18" cake base won't fit into it.