What's the best modern battery for my Duster?

That's for sure! Had nothing but trouble with those. Tried three different ones and none lasted more than a couple of months before they failed.
When I was still at O'Reilly, we had a battery shipment come in. It had six Optima batteries included in it. All six were dead meat. I put them on the charger. Not one of them charged up. They were all six bad right from the rip. When I was there, we had a practice of putting a volt meter on all of them to assure they had a charge. If they didn't they went on the charger. This was actually the first time we had any not charge up. All six had "MADE IN CHINA" right on them.