Both Chachas with high defense and survivability masks for maximum up time for distraction (such as Ancient Mask + Ultimate Mask) with skills to supplement this: Defense boost, Speedy Recovery, Seven Lives, Blood Brothers, etc. More importantly you'll want them to both use Rah-Rah + any other song for their Taunt skill (draws monster's attention when used) as well as slotting the Sneak skill into your own armor. That's about the most you can possibly do to have the lowest possible aggro time.
choose masks with "fast" recovery speed, and equip the skill "speedy recovery" on them the longer they're alive and around, the longer they can do their job you should also probably max out both of their "valor" values (max at 20), so that they always try to help, rather than running away from monsters
If you want aggro taken off of you as much as possible, the Ultimate Mask should be on one of your Shakas. That mask's main function is to distract monsters and keep the aggro on the shaka rather than yourself.