Unless you're doing some strict good karma role-playing, then yes, there's no reason not to hire MacCready. Regardless of how you feel about him as a character, his perk is more than worth it. If you don't like him, just earn it then banish him off to some empty, distant settlement. If, for some reason, you're worried about spending 250 caps on him, don't be. He'll end up giving you those caps back during a part of his personal quest.