Steele's record - 1 huge win
Priebus's record - 1 huge loss, 1 huge win, could still be re-elected after a potential 2nd huge loss
Hmm...I wonder which is better.
Steele was incompetent and if anything Republicans won in 2010 despite him, not because of him. And I remember with Republicans failing to retake the Senate, there was a lot of bitterness among them because of "wasted oportunities". I'm not claiming Steele costed him these, but he was no help either.
Priebus is very good at what party chairmen are supposed to do: coordinating fundraising and election strategy. He was doing a pretty good job as WI Republican Chair too. I wouldn't consider 2012 such a "huge loss", as it was actually pretty narrow. Then we have 2014 which was a real blowout.
Party chairmen have much more clout in downballot races than presidential ones, with a candidate's campaign essentially taking over running things on that level.