Of equal importance is the training of the installation tech. Sizing and setup are critical to the best operation and reliability.
I went with a Buderus unit and a Superstor Ultra indirect on my R&R. It's been three years now, and it's just purring along. It didn't hurt that the US distributor and training center is within 20-miles of my house, but I asked around and it got some of the best reviews. The guy that installed it had one in his home, which is a good sign, too. There are several others that are decent. I originally was thinking about the Weil McLain, but the contractor had had too many problems with the heat exchanger and wouldn't install the Ultra. They may very well have resolved that glitch by now.