Well they can both have the potential to beat each other. Sai seems a bit more professional while Jugo's got heavy duty to deal with. If he can enter Lvl2 willy-nilly he'd have a huge advantage. So far it only seems to be the result of when he's blood lusted. He can do a LOT more damage not to mention defense at the draw back of making the wrong moves at times (eg. rushing into suigetsu and paying the price). Around equal IMO... I forgot if we've seen how Sai's sealing works in the manga or not.