We always recommend absorbed glass matt (AGM) batteries because of their many advantages in a marine application. An AGM battery can be completely sealed, and the electrolyte is suspended in a fibreglass-like separator that will not leak and has virtually no gassing. This makes it a true “no-maintenance” battery, which means it can be stored in compartments where you could not place a lead acid battery. Lead acid batteries need clearance on top for maintenance and proper venting of the dangerous gasses that can be produced.
AGM batteries can also be charged and discharged more quickly than regular deep-cycle batteries (40% of their Amp hour rating verses 25% for lead acid), which is great for shorter charging times and higher current applications, such as for bow thrusters or a windlass. AGMs are also extremely tough and resist vibration. I have seen a demonstration where six 1/2” holes were drilled into a marine AGM (one hole in each cell), and the battery still started the outboard motor.
It is also a good idea to look into your power consumption and charging setup to determine why your old batteries died and if any additional measures are required to maintain the life of your new battery investment.