I never really had a training partner but back at home I would always meet up my friends at the gym at say 3 or 7 and do our thing. Now that I went off to college I just don't have the motivation to go to the gym and wish I had a workout partner kind of, or a good friend to go with me.
The different level thing is a hard one sometimes I like someone at a higher level than me so that they push me harder, you seem to adjust to what they do, but sometimes they push too hard and results in injury. If you have someone lower level than you, you usually feel better and bigger, but you prob dont push yourself and just settle for the weights that they lift.
Cons of partner go to fast or too slow is my main complaint. I like to do a set when my body feels ready to do one, don't like to be rushed and sometimes I hate waiting on them because I lose my pump.
Pro: someone to spot you, keeps you lifting hard