The difference is since the line of gravity with a front squat is infront of your body it is a more quad dominant exercise, rather than the back squat where the line of gravity is behind your body so it is more hip dominant (glutes, hams) and works your posterior chain. In a front squat you have no choice but to keep your torso straight , as you flex and extend hips,,in a back squat your torso if free to move forward (like a goodmorning) as you flex and extend the hips so your lower back can help you "cheat" if you wanna call it that, in a backsquat if you lean your torso forward the weight will fall.
This short article will help you with the benefits and pro's n con's of both---->
Front Squats vs. Back Squats | StrongLifts.com
Basically though back squat is going to allow you to use more weight and develop your posterior chain more effectively.. I would switch to front squat time to time just to change things up a bit or do some quad work... i would only avoid back squat if i had a lower back issue, or if i was just more focused on strength phase of training.