Do you "need" spill proof type battery like AGM?
To me if you are looking for the most Ahr for your money those AGMS are extremely expensive.
You can get Sams GC2 FLA batts with 210Ahr for $80 per 6V battery vs $210 (plus $32 shipping) per Amstron 210 Ahr 6V battery.
Sams 6V FLA costs $.38 per Ahr and Amstron is $2.42 per Ahr.
Something else to consider, there are several types of AGM, one is only good for 80% or less DOD (Depth of Discharge) and the other is good for 50%-60% DOD.
Compare that to Sams FLA GC2 which can be easily discharged down to 20% DOD without harm (although at somewhat expense of some of the life).
FLA can also be discharged 100% and as long as you recharge as soon as possible it will "recover" to some sort of usable capacity.
AGMs if discharged to 100% will result in expensive door stops (even if recharged immediately)
Granted AGMs are considered Maintenance free, that same characteristic can also be a downfall in the fact that if you overcharge a AGM it will vent the pressure and when that happens you lose electrolyte and can not add new electrolyte.
With a FLA if you overcharge it you can at least add water to it..
There are a lot of pros and cons to both types..
To me, watering my batteries is not a chore, I do it once a year and only takes 10 minutes at the max. So far no corroded terminals but I use a product called No-Alox which is a grease used for connection aluminum wire to copper wire.. It stops oxygen and moisture from getting to the connection and hence prevents corrosion. Been using that for years on my vehicle batteries with success..
You just need to ask yourself if you just simply want (and don't mind paying for)the "cool factor" when you tell folks you have AGMs.