Well, the Nissan will way outlast the komatsu.
They liscence the nissan engine etc., and make it in korea (or wherever) and in my experience, it's just not the same.
I have no idea why you'd be scared of the mazda's, they are the toughest little engines I know of.
The short story is, if you are not going to use the unit a ton everyday, then the cheaper brands will do just fine.
So I'd suggest tcm, hyundai, daewoo etc.
All the big brands will sell you a superior unit, but @ 188 hours/year, you'd never see the difference.