Both forced Ventress into retreat, Ki-Adi also dueled with Grievous for hours while exhausted. However Plo's defeat of Ventress was with a broken arm, so he'd likely have the edge in sabers. Ki-Adi likely has the edge in TK, but Plo Koon does have electrical judgement. Ultimately I give the slight edge to Plo. It can really go either way though.