You didn't say how big of a battery it is? At any rate, I would get the biggest battery series you can put in there. For me, I use size 31.
I would also purchase AGM batteries. They seem to last longer, will not deplete due to repeated charges, will not discharge, and can be mounted in any position.
As for Optima, I think you are paying for the name on that one. I would think that if you compare an optima of equal size to another battery of equal cold cranking amps, reserve amps, and so on, that you will not see much of a difference. For me, I use Cabela's AGM batteries. I own 8 group size 30 and 31 in three different boats. I troll at speeds of 1.1 to 2.0 with my trolling motor tournament fishing for walleye and can get 8 to 10 hours out of a charge with a 24v system. I don't have any optima batteries to compare it to, but, for the money, I really don't need to test it! Just my 2 cents but the contingency money optima pays in the event you have their batteries onboard and are the highest finisher is not worth the cost of buying them (in my opinion).