OP, this subject is being revisited again and again. Read maybe this recent thread:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27114481.cfmPrice of AGM varies a lot, can be anywhere from $160 to $ 300, for a 100 AH battery. And so is the life span. If you go AGM, try and get one of well known brands like Lifeline or Deka. I chose AGM for 2 reasons:
1) Longer shelf life - you can leave it unattended for 9-10 months without 120V maintaner. AGM have very low self-discharge rate. Flooded battery will be fully discharged and either dead or damaged by that time.
2) Ability to mount it "almost inside" - in the front through-storage under bed. Unlike flooded, they don't vent any gas unless overcharged - but overcharge rarely happen with a solar charger and when you charge from generator, then you are awake and can keep an eye on their state of charge (and open the lid to vent the space).
With any battery if you want it to last long, a good monitor like Trimetric is a must.
