I agree Newmar would be the first one....now as far as Thor and Winnebago, I would classify them pretty close to each other. First of all, we have owned to Thor products (TT and Class C). Very little issues and not really Thor issues, but more or less components (slide motor in Class C). I have a friend that had Winnebago and had to have an interior wall replaced, water pipes leaking under the bed, and the main door adjusted because they could see day light when inside. All those issues were not components, but build issues. Every manufacturer produces RV's with issues. Many people are against Thor, because they hear a lot of stories about issues... Well Thor is the largest manufacturer in the US of RV's. So based o that alone, they are susceptible to more reports of issues. But I would almost guarantee you that if you looked at it on a percentage basis, that they are not going to be any worse than their competitors. Heck my in laws have had issues with every motorhome they have owned. Even the $500k monaco they used to have had issues...problem being that their issues were a lot more costly.
Stick to what you like and check it out good. You will be more happy than worry about what everyone else is saying or thinking....