--Definitely go with gas
--If you have a large house, get more than one and distribute them
--Make sure the person who installs them actually has experience with the brand (if not, find someone who does)
--Go to each of your faucets, take them off, peer inside the fixture and find the water regulator (all new faucets have them to "save" water), take a pair of needle-nose pliers and rip the damn thing out of there (be careful not to damage the washer). Otherwise you may not have enough water flow to alert the heater of your need for hot water!
I had one in Europe that was awesome. But these days, everything in this country is made so "energy efficient" that it barely works for the intended purpose.