The breakdown for Monk's is simple. 2hander anywhere you may get aggro, thanks to staff block aa you have more natural mitigation with the staff. The argument for going dual wield is solid as well, thanks to aa's like Weapon Mastery of the Katori and Ambidexterity the Dual-Wield damage keeps up pretty well with staff dps.
Either way you go, monk is ideal with the fastest weapon possible. So that's 18 delay 1handers or a 23delay staff, this is to ensure you're getting the most crits, flurries and weapon swings per minute. With staff parses in SoR sitting ~90k dps higher from my personal testing on monk, I'd say ditch the dual wielding and go with the staff.
Other than those, the choice is purely cosmetic honestly.