I prefer to train with someone who has the same goals and mindset as I do. I found that if I train with someone who is stronger than I am, I will push myself so much harder because I know he will be there to encourage me.
I rather train by myself though if the person im training with has different goals. It does not work very well at all if we have different goals. He will want to do a bunch of abs and running and Im trying to gain weight and dont really care about my abs right now.