Josh Mandel is not a Christian (he is an unfulfilled Jew). This is a big negative for me. He seems to be Republican establishment candidate. That is another big negative. I have also heard that Mandel promised to serve out all four years of his term as Treasurer of Ohio.
The most of rest of the candidates have things on their websites which show they probably do not have a basic understanding of the constitutional separation of powers (i.e. the 10th Amendment). They promise things which they can't possibly deliver within the framework of the Constitution.