The last decade or so, I've been stuck on getting my batteries at WalMart. I buy their best one, in the biggest size that'll fit (more reserve capacity). Their best ones have a three-year full replacement warranty and two more years after that where they pro-rate the value. I've never had a bad one.
Toasty makes two very valid points about what he runs, one being dual posts, which I appreciate now that I bought a whopper of an inverter and will need to attach a set of 2 gauge cable to run the thing, but that also comes in handy for having an extra set of take-offs for an accessory bus or for having lugs/leads for a battery tender. The second point is using an AGM for the mess-free qualities.
Problem is, I'm cheap. I spend around $100 if I have a junk battery for a core (I always seem to be able to find one) and I run a power bus for accessory terminals right off the same connection the main harness uses. Scrubbing Bubbles takes care of anything that needs to be cleaned up.
John B.