Boosting works the same in vanilla as it did through TBC/Wrath. Your XP per kill does get reduced a lot with a level 60 in the group but it's still a lot more XP per hour than you can gain by yourself.

Mage is by far the best character for dungeon boosting.

As Alliance I generally go:
Deadmines 10 to 15
Stockades 15 to 21
SM:Cathedral 21 to 42
BRD 42 to 48

Boosting past 48ish gets slow because you need to kill much higher level mobs that start becoming too difficult for a mage to solo easily. At that point you're probably better off trying to gear up your group and just run dungeons normally.