(just off the top of my head)...
Reasons why I don't want Romney:
Romneycare (Obamacare must be repealed, and we don't need someone there who implemented something similar in his state and wouldn't renounce it)
His beliefs on global warming (what is the correct temperature of the earth anyway?)
Reasons why I don't want Perry:
His beliefs on illegal immigration
Sure, neither of them are perfect, but given the choice here, I'd go for Perry.