Coupla data points:
1. AGMs are currently about three times the price
of FLAs; and
2. AGM longevity (in "life cycles") is highly dependent on average depth-of-discharge (DoD)
If you contemplate using batteries in an application where they will be routinely discharged to more than about 50-60%, you're likely better off with FLAs as they will produce a greater number of useful cycles. And, of course, they're 1/3 the price
to begin with.
Typical AGM specifications for a 40% DoD, however, are about 1,500 cycles. Pretty good!
However, if it's both cycles and ability to be deeply discharged you're looking for, it's hard to beat the Rolls/Surette batteries. These FLA designs -- which are costly -- typically last over 10 years, way past the likely longevity of AGMs.
It's true that both AGM and FLA batteries deteriorate if left for long at less than a full charge (due mostly to sulfation, not stratification). However, AGMs have a much lower self-discharge rate, so you might be better off with them if you contemplate leaving the batteries unattended and not on a charger for substantial periods of time.
Newer, better technologies are in the wings (and are even now available on a limited basis to military and some industrial users). We can only hope that they'll be available on the general market in a year or two.
Meanwhile, FLAs are definitely the price-point technology. But, AGMs have a great deal of appeal for some situations, too.