I was lead to believe the depth of the squat (i.e. bollow parallele) has a possitive effect in bum toning but many would argue against it due to hip or knee pressure, I'm not on either side of this though so its entirely up to urself.
But squats are a great excersise, you could also consider lower back work and thigh work too in addition to a squat as to emphasise the toned results of the bum, this would make it look better if thats what ur after.
if you was interested in lower back id say deadlifts but they can be dangerous if done poorly and you need to use a good ammount of weight due to the low sets etc, so I'd say back extensions, standing twists for lower back and love handle area and dumbell side raises if thats what ur after.
As for thighs especially the upper lunges can bee great but try to get your form right before adding any weight (if your going too) dont want a achilles injury xD
then squats can be front, back or goblet, many would argue the possitive and negatives of each I'd personaly say find the one you like the most and go with it, gym work can go to hell once ya get bored of a routine xD
hope this helps