Optimas are not 'junk'...buuut the quality went down in the 90's once Johnson Controls bought them, and recently hit another low not that long ago when they closed down the plant in Colorado, laid off all the employees, and moved the entire manufacturing operation down to Mexico. They also changed the warranty, making it shorter, with no pro-rated period.
The 'BEST' AGM battery out there (and some would say the 'BEST' automotive battery, period) is, believe it or not, the Sears DieHard Platinum. The not-so-secret is that it's really a private label rebadged Odyssey, manufactured in the USA by EnerSys, the manufacturer of batteries for the US Armed Forces. The Group 65 battery is a direct drop-in fit for Explorers, and has a better CCA/CA rating, not to mention not having to use adapters or hold down trays or any of that. They also sell a Group 25 and 35 for Toyotas, but it's the same price as the much larger Group 65.
Adding to the value is that the DieHard Platinum retails for $189.99, while the Odysseys, the SAME battery, are upwards of $280-300+. Even BETTER is that the DieHard Platinum sometimes is offered for $170 with certain discounts (it's $170.99 online right now, with savings), or even $140 on sale at certain times. I have, however, seen Optima redtops for $140 at Sam's/Costco, so the retail price is almost even in that respect.
The real kicker in terms of value is the warranty. The DieHard Platinum has a 4-YEAR free replacement, 100-month (total, not additional) Prorated warranty.
All in all, the DieHard Platinum just blows the Optima out of the water. The only advantage the Optima still enjoys is a lighter weight for it's claimed amps.
Personally I switched from the Optima 34/78 to the DieHard Platinum Group 65 in the Explorer. It wasn't a huge difference in terms of cranking, but the peace of mind is from being able to get a warranty replacement anywhere across the country at the Closest Sears Automotive Department or Auto Repair Center that carries the Platinum line.
I had a fair bit of difficulty getting warranty service on an Optima (although the service in Denver was great, twice I received a new battery when a cell went bad just before it went out of full replacement warranty) in the past few years, and now it's so bad that retailers will only honor the Optima warranty if you bought it from them and have the receipt to prove it. I am through with that drama and will replace my remaining Optima with a DieHard Platinum when the time comes, unless some better option presents itself.
Optimas were okay, I don't regret buying them, and mine have given years of dependable service, and never left me stranded. I don't you can ask much more of a battery. However, I do not wish to do business with a company that has forsaken it's loyal employees, it's customer base, and whose greed motivated them to lower the quality of their product, while having the nerve to continually increase the price and finally reduce the warranty period in order to cut costs and increase the bottom line. The Sears DieHard Platinum goes in the complete opposite direction, with a high quality made-in-the-USA product, the LONGEST warranty on an automotive battery, and at a LOWER price. Personally, I don't think it can be beat, which is why I bought one.
As for whether AGM batteries are necessary...sure, they aren't. You can get a DieHard, Duralast, etc. wet cell for $79.99-109.99 that might last 6-8 years. But for me, the main benefit is not having acid and corrosion all over the place. 7-8 years of clean, corrosion-free battery terminals, cables, tray, etc. is worth the price premium, since it comes with a higher amperage rating as well.
