Jerry,
I have had 55 amp alternators for many years. I have had no issues with them. In fact I have just replaced my units. One last year and one this year. I got the same 55 amp units again. I have 1 4D battery for each engine. My 110v kohler generator no longer works and thus it's battery is removed and soon the genny will come out for weight savings. Hope to get a new one someday. Like Tim "the tool man" Taylor would say, I would think the more amp hr power the better. I also have a built in battery charger so that when I'm plugged into shore power I can keep my batteries up. This takes the load off the alternators. Bonaventure lives on a mooring so I'm not always plugged in. I am plugged in during the winter so the batteries never get down too far.
Not sure this helps, but that's my setup.
George