To be honest I think the differences between Dometic and Norcold are so great that if I had to choose.. I'd toss a coin.
Norcold does have a product line I find very, very, very, interesting (This is a dual voltage 12/120 volt, unit, compressor type, like your home fridge, but thanks to the special motor and pump the light bulb uses more power (When on) than the compressor does when running, That is one impressive fridge, I have it's little brother an Engel Chest freezer, 36 watts and it can freeze 43 12 oz cans of pop) or the same volume of other stuff) It is their most expensive product line though.
Other than that, It's a coin toss, the technology is identical.. Dometic, for a while, had a problem with one of the components (But that could just as easily happen to norcold) I'd call them six of one half dozen the other