Set bonuses from Monk sets could require using 2 fist weapons.
The passive Guardian's Path could be a decider as well on 1H vs. Faster speed also means faster spirit spending with things like LTK to ultimately gain more life from Transcendence and life/spirit item mods. In addition, the faster attack speed allows for more Critical Hit and other on-hit procs, so if your build relies on crits (WotHF Blazing Fist, etc.) it's better to use 2 one-handers. Monks will almost always be better off wielding 2 one-handers (fist weapons), simply because 1 dexterity is 1% increased damage and you can get double the dexterity from dual-weilding.
