Explanation:

But: except; apart from; other than.
Rather: used to indicate one's preference in a particular matter.
Than: These two words are very close in their appearance, but than vs. then have very different uses. Then is commonly used to express a sense of time or what comes next or used to be. Than is used to form comparisons between two things.
However: used to introduce a statement that contrasts with or seems to contradict something that has been said previously, in whatever way; regardless of how.