I use altoholic, but I usually do the comparison on the alts themselves. Keep in mind that there is also a data sharing feature built in that allows you to give all your toon data to someone else with the addon. I haven't tried it, but if you keep the main updated with each alt, it might be possible to do a comparison for those accounts as well.

I just haven't played with it that much to determine if its possible. Also probably requires frequent manual updates to the main anytime equipment changes on an alt. Also probably doesn't handle dual spec comparisons very well (if at all).