That said ^^ (agree), I usually buy a biggun. 600 to 700 cranking amps is good. I like to buy deep cycles for any boat use -- think some are marketed as combined starting and deep cycling. When it gets old, I use it in the shop and buy a new one for the boat. There's mixed opinion on use of deep cycles for starting batteries, so may get different opinions. Depending on what boat you run, might want to go to a two battery system if you don't have one -- starter and house battery.
got burned a little on this recently (large deep cycle) because the battery I'm using is physically too big/heavy for what I should have -- need to move it around to put the charger on it, and would rather not do that. So smaller would be better in this particular case (mine).