Ok, I will go against the train of thought here. I would not buy a sealed product and in fact I did not when mine needed to be replaced. Yes there have been issues with flooded lead acid batteries and case leakage (GM Delco batteries) in the past but overall they hold up much better than absorbed glass mat or other "sealed" technologies. There are probably more sealed marine lead acid batteries at the bottom of your lake than flooded product.
Buy a good one. Look for, if I my suggest, a brand from East Penn Manufacturing, they brand name for a number of companies. The product is made in Pennsylvania, a family run business. Distributed in Canada by East Penn Canada (Power Battery Sales).
Flooded product will take more abuse that our particular cars give a battery with discharges and re charging.
IMHO.