Mesa
Sorry about your situation. I had a friend who was at Piedmont who resigned before his check ride, fearing that he would have the same issues you had with the single engine stuff. He literally got on with Mesa a few weeks later now going to the 175, he used his training in the 145 to get ready for the bigger better Embraer 175. He loves the training and culture there. Just my two cents. They have a culture of getting people the training they need.