There are a host of pros and cons to training with a partner. I have listed a few of each, which can help you in the process of deciding whether to train with a partner or not and a little aid in the selection process.
On the pro side, a drill sergeant of a partner can infuse intensity, motivation, encouragement and focus to your session-yelling is optional, but not encouraged ;). A scheduled meeting time together will also decrease the chances of skipping a workout, cause you to show up on time and keep you accountable. A conscientious and attentive partner can assist by providing a spot when needed and help blast out a few extra assisted reps.
On the other hand, an unreliable, non-punctual training partner can cause you to sit waiting to begin your workout, or even worse, skip it. An unmotivated, unfocused, chatty partner can have the same effect on you and slow down your session, deter you from your game plan, or cut it short. A partner who falls asleep at the switch (not paying attention) can endanger you if you are expecting a spotter.
Who would make the best training partner?
 It is less important to find a partner who is the same gender and strength and much more important to select someone who has similar goals, drive, intensity and schedule, to make it work over the long run.
Training with a partner can have advantages and disadvantages, depending on your selection. Training on your own can be fantastic if you are a great self motivator, however, a solid and reliable partner can be much better than training solo and can help to take your workouts to the next level!