Haste vs Double attack?

really?
If you want a multi-attack build then grab this WONDERFUL atma called Voracious Violet or Atma of the Apocalypse
as for outside abyssea (not sure what there is to be fighting at the moment) I'd still use full haste

Also if i remember correctly Saber Dance makes your DA rate unaffected by gear, which would make stacking DA gear useless, and in return, make stacking haste much more important