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Saltheart,
I can't answer which is more efficient,forced hot air VS forced hot water,but I can tell you this.For one forced hot water will not cause winter nose bleeds as much like forced hot air,alot of the high efficiency units are condensing which wicks moisture out of the house,but if you add a steam humidifier by April air or Nortec which get costly because you will be needing 208/230 volts to energize a heating element to generate steam,if you go with a cascading pad system and installed properly this will ad sufficient humidity to the dwelling area,you can also run a 24 volt pad & wheel system as well April air,Auto flo ect...
There are two things to conceder one for the humidity to stay in the occupied area the t stat or room temp must be kept at 68* or greater anything less than that the humidifier will be useless.
Secondly these must be maintained or you will get mold or the unit "might" not work right on the next season because the water in the cylinder,pad or tray has now crystallized and will harden on moving parts or heating elements.

As for AFUE results in best efficiency they can debate it,I think there are a ton of scenarios such as house insulation,windows,basement windows,bulkhead,doors/jams,attic insulation,rafters insulated or not,ridge vent etc.there are some many things to conceder.One thing about a furnace is when the burners turn off the fan relay can stay on for 30-60-90 or 120 seconds after the fact this was implemented to optimize efficiency but most say it's blowing cool air after the heat has disipated across the heat exchanger.
As for a boiler when high limit has been reached the burners turn off but the circ pump still delivers hot water,then if the t stat is satisfied it will not call for heat,but the baseboards are still radiating....So again I honestly cant answer your question but just give you my observation.

On a side note if you have allergy's there is a product out the called Guardian air it was created back in the early 90's to combat the Sars virus /bird flu this is a neat UV lite that gets installed in the supply air plenum it works off of 115 Volts and should be tied into the fan relay,this way it will get energized when there is a call for heat or cooling,anyway this product creates good Ozone and it is proactive google it and check it out,I think this it the best product one could have if they suffer from allergies.