A top DPS class will and always will be heavily reliant on situational fight mechanics. Unless a company just has absolutely no idea on balancing (which honestly its 2013 and it shouldn't really be an issue being this far progressed into our gaming technology). A BLM/SMN will edge out in fights that require a lot of melee adjustments and a stable ranged still rate. Your MNK/DRG will edge out in tank and spanks with ranged having to be mobile. Of course this is assuming that your character's are knowledgeable in their class and geared accordingly. With the way most games are set up, you will have an equalish mix of both kinds of mechanics so as far as a choice in picking a top DPS, it's really a matter of your enjoyment of the playstyle. You will win some lose some no matter which way you go.