Agreed. Optima used to be decent but since switching the manufacturing to Mexico several years ago they haven't been worth much. For the way you describe using the truck, with it sitting for a long time between uses an AGM is a good option as they have a lower self discharge rate and make a good deep cycle battery, but keep in mind that they have specific charging requirements to get the best out of them. The Sears Platinum batteries are actually re-labeled Odyssey, and I agree Odyssey is a good battery. The crazy part is you used to be able to buy the Sears version cheaper than the Odyssey version.
So I would recomend a deep cycle style battery regardless of which architecture you choose (flooded or AGM)
I would recomend the largest physical battery you can fit, at least if you aren't going to change to a dual battery setup. I don't know if you can fit it, but that probably means a group 31. Do be sure to check both the CCA and amp/hr rating when comparing, but be septic all of the cams of some of the off brands. When in doubt, look at the weight. Amp/hs only come with more lead so all things being equal heavier is better.
Make sure you have no parasitic draws. I hate tracking that stuff down but if you have some random draw any battery will go flat.
Consider an AGM but carefully review the OEMs charging requirements. You may need to buy a specific charger or change your regulator to get the most out of it.
Regardless of what battery you go with, I'd strongly consider getting a battery tender (of whatever brand) to maintain your battery while laid up. That will go a long way toward prolonging the life of any battery.
'07 LR3 HSE/HD - slightly non-stock
'96 D1 - even more non-stock