I'm very sure that Namine would be one of my best friends. I bet whenever I would feel like I need someone to just talk to (no matter what) she always be around to listen, and we'll just have great times doodling stuff. Ephemer seems like a pretty chill guy and also not too cocky. Think I'll get along well with someone like him & Demyx, Ienzo, Luxord & probably Axel/Lea.
But to be honest, I'm a pretty adaptable person so I don't strive to make enemies. But if there's someone that will just try to bring down the mood for sake of pain, you can bet that I won't be as generous. So someone like Vanitas constant insults, would leave him think twice.
Maybe I'll just be seen more with people like Namine, Ienzo, Ephemer, Riku, Luxord they seem like a nice group.