Anyone have experience with AGM or GEL deep cycle batteries?

When looking at batteries I think you should start with your requirements and work from there.
I have posted a few questions you need to ask your self before making the choice.
What you want to run and for how long?
How and how often will you recharge?
The size of the battery bank; Amp hour / turns into recharge rate?
How many cycles do you plan to get / % of a normal cycle / % of a your max cycle?
Auto starting genset with large charger to limit the % of discharge?
Temperature of where the batteries will be kept / ventilation / how much added heat from charging?

Glass mat batteries can have issues of shortened life if they are discharged past 25% often.
If you plan on glass mat then you will want an auto start genset wired into charger. A good inverter / charger system can handle this, but you have to look at your genset size depending on the brand.

Wet cell batteries are a PITA to fill, but they have filling systems for the better brands that make it simple and takes away a lot of the danger. Better to use RODI water or distilled water. Not as picky to large / deep discharges. Will need to be equalized a few times a year.

Wet Cell: you have to clean and water: Long life if properly cared for. The most popular is the GC-2 Golf Car battery (Six volt you use two in series to make one BIG 12 volt battery) and these are ideal for RV use.

GEL: NOT recommended, in fact finding GEL cells in the 100 amp hour and up size is kind of hard to do. They used to be popular back in the 70s in smaller sizes but not so much today... They have absolutly NO advantage over AGM and a whole lot of disadvantages. They are very picky eaters (If you charge them too fast you replace them tomorrow) I give them my very strongest negative recommendation.

AGM: All the advantages of GEL (low maintenance, no battery is 100% Maintenance Free) can be mounted in any position (No "This side up). Some makes (LIFELINE) can be recharged very very fast. However much higher cost than flooded wet cells (Roughly the same as Gel).

I have used small Gel's and was not all that happy with their life, even though they had custom made chargers designed to baby them.

About a year after I got the RV I bought a pair of AGM's put them on their own loop (inverter took care of them) and ... They were the first batteries I replaced.

I still have the factory Six Volt Flooded wet cells in place, still going strong. Rig is 8 years old.

I am not a fan of Gel-Cell batteries. Without going into a long explanation about their charging requirements, suffice it to say they are the poorest choice in my opinion. I am sure someone will address all the pitfalls for you but I havent had my coffee yet.
AGMs are my choice and I have been using them for over twenty years now. They are the most expensive to purchase, but are in my opinion the easiest to maintain and most trouble free, without the charging requiremants of Gel-Cell.
I will add that if AGMs are over charged and gas off they are pretty much toast, but then so are gel-cells.