There are so many learned opinions on this I hesitate to put in my two cents but I have never claimed to be oversmart. I was a good IMHO marine
electrician and I have installed more batteries than I can ever remember and have seen the goods and the bads of both batteries and the TLC, or lack thereof, of all kinds.
Basically - AGMs are great if you manage them right. Ditto for wets. AGMs are fundamentally different than wet cells though and any opinions to the contrary are suspect. Again IMHO. All batteries like to be charged to 100% and often. Do they need to be charged to 100% daily - no way.
I'll get to the solar issue next, but AGMs charge faster and will take stronger charges than wets. They are MUCH lower maintenance
. All batteries should be monitored 100% of the time though. You need to know where your batteries are and act accordingly. Charge at 12.3-12.4v and not at 12.1v. Lots of other do's and don't's. AGMs can take far more abuse than wets. They can last longer (and do). The people who hate them have either not used them or have not maintained them right or got some bad batts to start with (it happens with all makes, models, types unfortunately). Wets are a true pain in comparison. They have to be mounted upright. They not only have to be monitored by meter but also by water
level. They produce nasty gas when charging and most always get corrosive liquids outside at some point (they need liquid tight enclosures). They are very good batts though - if sized right and maintained right and high quality to start with. They won't have as many duty cycles. They are not as efficient charging. They take longer and more amps to charge than the equivalent wets. Good wets are way better than bad wets though. Quality matters.
Re solar, or other partial charges: We had lots of solar with a Morningstar charge controller and AGMs'. We cruised extensively and used our batteries and the solar was a BIG help. The solars may not top off the batts but they put in amp-hours that you don't have to add with your alternator or genset. They are a plus in any situation but the charge must be regulated to the battery type. More the better as far as watts but there is always a limit (space and $$). Even small helps. They will only 100% charge a battery if they give out more amps than you use - math. If the batteries are not being used they will top off and maintain the 100% charge. They can even equalize the batts if you have enough sun and watts (and the regulator
supports that mode). They will overcharge without a controller - huge voltage will fry any type of batt.
Our latest (5 weeks new) cruiser came with AGMs of unknown age. Also solar with an Outback solar controller. The controller is not set and/or working right though as it is charging to too high a voltage. I am sorting out the boat just now and that is a priority on my list. Massive solar and three 8D's (more than we need actually). Also a 275A alternator/genset. And a 100A alternator on the auxillary. You need a high output alternator for a large amp-hour bank, especially AGMs otherwise you will never keep them charged and you will likely burn out the small alternator. Wets aren't as destructive since they don't charge as fast but it is then harder to get them to 100%.
So absolutely solar is a good investment - the more the merrier. Good regulator
, set right,is essential. Alternator sized to the batt bank with a good regulator set right. Monitor the heck out of the batts when using a lot. Keep them charged whatever type. AGMs are expensive but best IMHO for cruising - more use cycles and easier to charge. Wets are great too - just a bit more work and they charge slower for same output of alternator and/or solar. AGMs are more tolerant of low charges but no batt likes that. If I had good wets I would keep them and love them. It's a trade
off as are most things. I can't afford the best of most but I splurge on batteries and battery systems. If you go from marina to marina and use AC to charge, it doesn't matter so long as it is well regulated. Ditto for short cruises between marinas