All Ace addons are now being supported and hosted by Curse. I use wowmatrix to update all my addons, its searches curse, wowinterface, ace (even tho they are on curse now) for all updates. Only problem I have had is patch day and a few days afterward due to the massive amount of bandwidth being used on all the sites.

One addon I highly recommend is Jamba. Its essentially a one stop shop for all your multiboxing needs. It can be found in the macros/addons section of the forum. Its supported very well by the author, and open for suggestions. Check it out.

Beyond that, addons are up to your preference and playstyle.