AGM batteries if you ever plan to crash your bike--or drop it hard--and/or aren't very good at watching water levels in multiple cells while trickle-charging all winter. I'm never going back to wet cell batteries, and haven't seen any reason to try gel batteries.
About brands, I haven't a clue.
Edit to add: Forgot about the Li-ion issue. I haven't yet been convinced of the need to spend extra money on a battery which I can so easily destroy (by running it down) and which forces me to buy yet another battery charger as well. But that's just me, and I need the extra calorie burn from hauling a heavy battery around with me.
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