Rinnai Continuum
i've got a Rinnai Continuum propane H20 heater and i am pleased with it.
initially expensive, yes. possibly paying more for the Rinnai name.
however, i wanted a tankless that would handle major-load hot water demand, and it does this very well.
i live in southern vermont and don't have any complaints about the temp of the water, any season.
if you're budgeting for one, know that the Rinnai requires 3/4" pipe for the supply coming in from the water source and leaving the unit - not 1/2" - so you may have to upgrade your plumbing in that way (i did ... again, an initial set-up expense).
i researched this purchase a lot before choosing the Continuum. talked to a number of folks who own them in the northeastern US. i'm glad i purchased it, and i also know it wasn't an inexpensive choice in the short run. over time, it more than pays for itself.
good luck!