Most of us are not very happy with the gel batteries. They don't seem to hold up as well as they used to. Apparently the manufacturer changed hands and the building process changed. "New" means new. It doesn't always mean better.
I prefer the largest that will fit and for me it's a must that it's NOT maintenance free. I WANT to be able to add water if needed. There is a very good argument for going to a tractor supply type store and buying a tractor battery. They seem to have heavier duty plates and more rugged cases. If you don't offroad, this means nothing.
Stereos, winches, etc. pull their power from the battery which is then backfilled by the alternator. So if you have this kind of stuff, the more reserve the better.
Be kind. If for no other reason, it will confuse the daylights out of people and make them wonder what you're up to. And ALWAYS drink upstream of the herd!