"I'll go with the candidate I'm used to" or "I'll go with the candidate to whom I am used?"

Solution 1:

There is absolutely positively completely nothing wrong grammatically with ending a sentence with a preposition. This was a bogus rule made up by grammarians to sell grammar books, and ignores the way Germanic languages work. Some people cling to the rule, but it is a question of style, not grammar.

Furthermore, used to has become, in practice, a lexical element, which is not easily split: "to whom I am used" is awkward and may be misunderstood.

Thirdly, "go with" (in this sense) is a colloquial expression, and does not match the formal nature of "to whom".

I'll go with the candidate I'm used to.

every time.