OK, I'm not a battery expert, but I'll share some opinions.
Our battery trays are pretty much filled up by the stock batteries, and finding a replacement with the same (or better) CCA and RC that will fit the available space has proven to be more difficult than I would have expected.
Due to the design of the Optimas, I think that you can expect superior cranking amps, but they clearly have less reserve capacity, UNLESS you go to the Group 31 size. That might require MINOR battery tray modification, but the main problem is cost - approaching $250@ with shipping on any website I could find. I couldn't find blems in this larger size, at least not yet. Reserve capacity is a legitimate concern for those who must let the vehicle sit for long times, or those with ESPAR's or similar accessories they need to run when the engine is not running.
I want the sealed, AGM-type battery, to avoid the post corrosion others mentioned. But this "sealed" battery brings another consideration - charging voltage recommended for a "float" charge is <13. 8 volts. Most of our alternators are putting out more than 14 volts, even after the battery is fully charged. Those who draw the battery down with short trips may never see a problem, because it's OK to charge at higher voltages for short times or when bringing a discharged battery back to full charge. But those with a lot of road miles may overcharge the "sealed" type batteries unless you find out how to tweak (lower) the voltage output of our alternators. This could explain why a few members report less than stellar results with the Optimas, while others love them. As they say, YMMV.
Right now the most likely candidate for under my hood is the WalMart MAXX-1N (not available in some areas) or the Autozone Duralast Marine (1000 MCA, CCA unknown but probably 800+, and RC=180 minutes. ) At $55, I may just have to clean the terminals once in awhile. Another one I'm still researching is the ACDelco Professional Platinum battery; it's another type of sealed AGM battery, but so far if it is available in a Group 27 size to fit our trucks, with enough CCA and RC, I haven't been able to find one. I suspect it is new enough that our size isn't made yet.