One installer recommends crown but not the high efficient model because they don't believe the high efficient models are reliable over time. Another installer says crown is a lower quality boiler and the Knight high efficient model is the way to go. How long can I expect a regular boiler to last compared to a high efficient one?
mod/cons have been around long enough now that it should be clear that they typically last long enough to make them worthwhile. the efficiency difference is quite significant compared to a non-modulating boiler in most cases.
The reliability of a boiler like any other appliance is a reflection of the initial installation and the preventive maintenace. I have seen some of the best fail as much as some of the worse. It's all about who and how installed.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."