Last week I replaced the 5 year old red tops with shiny new ones. The engine cranks much quicker now.
One reason I ponied up for the red tops was the fact that they don't gas when being charged. It's what came stock, so I guess there's a reason for it.
Gassing = corrosive vapors and spill-overs. and I mean cor RO sive. No broccoli on the terminals with an agm.
Another reason is their long term cranking capacity. After 35 years as a mechanic, I have put many batteries to the test. The agm batteries just wont quit giving voltage, or amperage.
When you have a starting issue, you NEED a good battery. Everything is hinged on it. I've seen 20 below F here before, and when I need it to start, it HAS to start.
That being said, if you do opt for a conventional battery, most of my automotive customers get an Interstate Black Top (Megatron Plus). A bit pricey, but the best battery around with a very low failure rate.
We have warrantied 1 MTP in the last 5 years, and that was actually due to mis-use by the customer, but my rep was in a good mood that day.
Don't get me wrong, if you're ok having to swap out batteries when the juice goes out, use whatever you have, just don't rely on it starting when you need it to start.