Hm, it's hard to say how strong Saa gets... once rooted, her Battle Meditation was seriously impressive. Her final energy-control was impressive too (though as that was at the cost of her life, it was arguably a 'oneness' moment).
Non-rooted, she had good TK, uprooting and throwing trees, but that's the extent of her *known* offense.
I'd say Nomi, though part of that is the unknown of if T'ra's offensive abilities increased a lot too after she rooted.