Avoid OS and LH in Y. 30 inch and 31 inch legroom is bad for a long international flight. UA might not have the prettiest cabin and the best food, but E+ makes for a much more comfortable flight for me. Munich is an easy airport for transfers. I usually fly IAH-MUC-BUD for trips to BUD.
IAH-FRA-BUD can get you on a 787 and is only a little more difficult transfer because of the very busy FRA.