In my opinion the choice is clear. I would install a tankless hot water tank
in the small closet, thus opening up storage. Remove the boiler and go with the forced air gas unit in the attic.
As far as brands go, they all are good. The one to avoid is Janitrol. I prefer Rheem, but the most important part is to choose a reputable dealer. A quality installation is more important than brand. Whichever brand you choose, go with a 90+ furnace, sealed combustion that uses outside air for combustion. Carrier, Trane, Bryant, Lennox, Rheem all strive to have the better dealers carry their products. Therefore, usually, a dealer that specializes in one of those products is a good choice.
I have installed many units in the attic and I don't understand how the choice could be different. Hot water heat is not as good as they claim. There are many advantages to being able to filter the air. Have a top shelf air filter/cleaner installed and make sure you change/clean the filters monthly.
My preference is the Honey Well Electronic Air Cleaner. Do not forget to clean them!!!