[tom the eldest]

Saruman would probably be a good ally.seeing his extensive knowldege of dark arts and sauron's trick would possibly help the west a lot.though for sauron's allies(easterling,variags,haradrim,etc)he is useless


Edit:and his persuasion voice could maybe influence the nazgul and give them false information about the west plan.even if the nazgul see isengard destruction,saruman could still wriggle his way out from the nazgul.