12v Vs. 120v burner system

Next month we are planning to upgrade our washers. So, I would like everyone's opinion on the advantages or disadvantages of the two systems. We currently have 120v systems that are separate for the washer(add-ons). We plan to purchase self contained hot water units.

I have had one of each, 120V and 12V. Started w/ a 220V, using customers hot water.Not very satisfactory. I upgraded to a Honda powered 120V hot water machine, using an Onan GenSet for 110 voltage, that just meant two engines to work on. Last August I went to a 12V ***** , no real problems so far, and only one engine to maintain now.