On Rosh Hashana, we traditionally go to our family’s house and have a big dinner, then go home. Would it be wrong to go to a friend’s house (who is not Jewish) who is having some friends over to hang out (not Rosh Hashanah related)?
It is not clear from your question why you are favoring going to a friend over joining family. However, as a general rule, one of the methods G-d tells us to employ to sanctify our holidays is to eat several fine meals with people we are close to. These meals should be eaten with a feeling of appreciation for the opportunity to celebrate G-d’s closeness to us. Through these meals, we motivate ourselves to continue growing and becoming better people. Based on this, it would seem that you should seek out whatever meal will help you sanctify the holiday best.
If you are puzzled, as many people are, as to how a family dinner can be synonymous with sanctity, I must suggest that you try joining an observant Jewish family for a Shabbat meal. Although it is impossible to generalize, many observant families put great efforts into giving their festive family dinners a degree of holiness. I could make arrangement for you if this is of interest to you.
Happy & Healthy New Year
Rabbi David Shenker