[Guildo]

Tuff question to answer they where all Maiar the Balrogs where Maiar of Melkor, Sauron was a Maiar of Aule ( but converted to Melkors side, and the Istari (Wizards where Maiar of various other Valar) i think the deciding factor here is that the Istari where only given a certain amount of power by the Valar and Lluvitar based on Sauron's power. the Valar did not want any one of the Istari to defeat Sauron by them selves, but rather work together to bring down Sauron. Now The Balrog where created directly by Melkor and where not given a limit to there power (with the exception of not becoming more powerfull than Melkor himself) so its very possible that the Balrogs could Acheive more power than the wizards. Sauron was a Maiar of Aule who Melkor talked in to coming to his side, Becouse he was Melkors right hand man, he took over the thrown so to speak when Melkor was sent to the Void, and Sauron had all the dark minions under his controll, and we see just how powerfull he became.

Feel free to correct me if im wrong this is just my two lembas worth.