I like the AGM batteries,
no corrosion on the terminals.
They are expensive but may be worth it to some.
Especially those that need or want the no spill feature of them.
Also as far as getting to "big" of a battery and having the battery out run the charging system,
that's a new one to me.
As far as I know the only way to get a charge deficit is to use more energy then your system can put in and that will not care what size the battery is.
We have had 900 cca batteries in a IH 560 with a 20 amp generator.