Is the OP Tandon book best for theory of organic and inorganic chemistry? Also, is it best for physical theory?

For physical chemistry, go for RC Mukherjee. Personally, I think it is one of the best options available.
As far as OP Tondon is considered (for organic) , it is only good for learning new concepts and stuff. It doesn’t have that good a question bank for practice. I would recommend Himanshu Pandey for organic chemistry, if you really want to practice good JEE level problems. And for inorganic chemistry, NCERT will be good enough.