Boilers are becoming more efficient every year. They all need maintenance and upkeep.
Some boilers have cartridges that need to be oiled. Over-oiling will damage the circulator . Tankless boilers condensate into a trap . The trap should be service yearly to avoid boiler shut down of leaking.
The heat exchanger should be cleaned yearly. A professional should be doing this work . This is not for homeowners to practice on. You could cause damage to your boiler or you could cause an explosion.
Boilers are a good choice in heating. I personally like radiant heat because it is quiet, it maintains the temperature in the room making rooms more comfortable . Boilers last alot longer than forced air furnaces . Average life span of a boiler is 20-30 years. That is if you keep it tuned up every year.
Also if you are thinking about purchasing a new boiler system . You may want to do some research on Weil Mclain and Burnham . These boilers are the leader in the industry. In Northern Colorado they are easier to obtain repair parts for too.
If you live over 6500 feet there are other upgrades that need to happen. Like a high altitude kit, propane, whole house water filter and condensate neutralizer.