Can I use 'might as well' instead of 'would rather' because I think they have similar meanings?

Native speaker’s answer
Rebecca
The connotations of the two are actually quite different. "Would rather" implies that one has a preference for something over other choices, whereas "might as well" is usually used to imply that one is making an undesirable choice or doing something in an unenthusiastic way. Thus, using "might as well" here would completely change the meaning of the sentence (turning it into: "I'm here with you now, but I'm not enthusiastic about it"). Ex: I would rather have a quiet dinner at home than go out. Ex: I might as well throw out the garbage on my way out.