cone size won't matter at all if the subs are in the correct boxes. The whole "10"s sound tigher and 12"s are all distorted and loud" debate is a bunch of crap
2 10" subwoofers = more cone surface area than one 12" so technicaly two 10" woofers have the potential to give out more bass than one 12"
So if you have the money go with 2 10" subwoofers, get quality ones and if you listen to mostly rock I would recomend around .75-1.25 cubic foot box, sealed for each 10. That will give pretty good bass response and when paired with a slightly larger then normal box you will get pretty good volume as well. Run the subs at their rms and you should have a pretty good system.