I agree with Fang ... it all depends on what you will do with it. I own an Optimax 225 and at this HP level I think 2 strokes are better. But in the 115 HP range, a 4 stroke could be better, especially if you will put in through double duty such as trolling. Fuel consuption at WOT are almost identical, with the Opti doing a bit better, but at slow speeds the 4 stroke wins out. And as Wayne says, the 2 strokes need room for the oil resevoir. Opti's require a bit more maintenance which means added cost but then the 4 stroke costs a bunch more to buy ... a toss up to me. Neiher produces noxious smoke so again, a toss up.
So, now that I've confused you more then before, I'll tell you what I would do. I would opt for the 4 stroke only because I'll assume that will you're not be getting a kicker motor for trolling. The problem with trolling with a 115 is that you may not be happy with the speed, it'll troll too fast. But you can get drift socks to slow you down some and this may solve that problem. The trouble with socks is that it is hard to make turns. Ideally, you should also rig your new boat with a kicker but that adds more dough to the price tag.
I guess I still haven't helped you, sorry.
Hookset, just read your latest message. The brochure is, flat out, wrong! The 2 stroke will be significantly faster on a bassboat.