Which type of person should I try to make friends with?

Well I am going into middle school next year and I just want to know which type of person to try to make friend with. So let's say I am in the lunch room and I want to sit down next to someone I don't know and make friends. Should I sit down next to a group of people who seem to already know eachother, or someone who is alone? I am a girl by the way. I was thinking that if I sit down in a group, they might be mad at me for intruding. But if I sit down next to someone who is alone, they might be grumpy and that's why they are sitting alone. So what should I do?