The Navian combi is a good unit, but, none of the wall hung boilers - especially combi units are really as durable as cast iron. But, if you don't plan on living somewhere for a long time a high efficiency wall hung combi unit makes sense. IF you're on natural gas where the efficiency difference won't make as much of a $$ difference, and you plan on living in your home for a long time a cast iron 80%+ boiler with a domestic hot water storage tank on its own zone would be the way to go.

As far as brands (Cast Iron) I Haven't had any issues with:

Burnham
Dunkirk/Utica
Peerless
Williamson

For combi and/or high eff. units:
Navien
Laars
Peerless

Many of these companies have had issues with a particular model of boiler, ususally a high eff. model, that they've then straightened out. So you really have to get some estimates and do research on the models quoted to see what they're track record is. Brand is less important than model and installer.