I just went through this buying my first Optima batteries. A 12V red-top for my dad's '32 roadster, and a 6V red-top for an original 1929 roadster. I had a hard time finding the 6V, they were on backorder everywhere. Yesterday, I cancelled my back ordered Jegs 6V battery because I saw Speedway finally had them. They shipped it today. They always have excellent service.
I chose the high-end charger Optima sells, I bought it directly from Optima (not cheap). The only problem is it's only a 12V charger. I figured they would know best how to charge their batteries. You just hook it up and leave it and it will maintain the battery. As far as I could find Optima does not make a 6V charger which I thought was a little strange. Every good battery charger I've ever had, had the 6V or 12V setting. From what I read the main thing is to charge the AGM batteries with low amperage, too fast of a charge causes it to gas and you lose the liquid which cannot be replaced but tha is the same with any sealed battery. The AGM chargers have programs built in to revive an AGM dead battery that regular chargers do not. So, I will be using use my new Optima charger on the 12V red-top to keep it maintained and charge the 6V every once in a while, with a low amp motorcycle battery charger.
I chose the 78-34 dual post red-top. The reason why is the battery is in the truck of dad's 32 roadster. The side -mounted terminals will allow the starters' positive and negative cables to go straight down through the floor for a cleaner installation (the holes are already there so I'm using them. The entire starting system will run off of those side posts terminals. But I will still have the top posts which I can use to power up the rest of the car. I thought it was neat way to wire it all up neatly. I'm just now starting on that project along with cleaning out the gas tank. I have had pneumonia for two-weeks which has kicked my butt! I keep going out there to work on it, but my chest hurts too bad, and I can't get any air. Its slowly getting better but I think I need to swap out the intake to my lungs to a three-carb? They checked my heart out, no burned valves and no plugged fuel lines.