Largely agree with the above, with a couple of things to add.
It could be argued either way as to whether or not Andy Ritchie has been a success anywhere he has been. I would say though that, unlike Sheridan, he has a League 1 promotion on his CV. I also think he was harshly dismissed from the job here. However, I still wouldn't hope for him as manager again.
If I was picking an ex manager to come here, it would certainly be Dowie. He was a success, he wasn't sacked and he didn't disrespect us when he moved on. So long as he still had the passion, he'd be a good appointment I think. Won't happen though.