One thing to watch out for these days, when comparing specifications, is the increasing use of "cranking amps" either in addition to, or instead of, the "cold cranking amps" rating.
Cranking amps (as well as Marine Cranking Amps) testing is done at a higher temperature (32° F I think?) than cold cranking amps (taken at 0°F), so the numbers are higher on paper, even though the battery would be weaker than one with the same number of cold cranking amps.
In other words, if it says "900 cranking amps" on the label, it's probably only got 750 or so "cold cranking amps" and is therefore less powerful.
Reserve capacity as far as I know uses the same criteria across the board, so a battery with 120 minute RC rating is still longer lasting than one with 100 minute RC.
Either way, more is usually better. Just watch for how it's worded.
Paul