This is a tough question since you don’t always get a say in who is available to work with. But as a general rule, it is easier to work with people you have a good relationship with until you fundamentally disagree on something and cannot make a compromise. Also, you may not have friends in all departments and will eventually need to work with someone you don’t get a long with, but becasue you’re working in what should be a professional enviornment, you should be capable of reaching a decision.