I'll be blunt about this assuming you're a student. Roll a awesome easymode character like hunter or warlock. You level and farm easily. This helps A LOT if you're a casual player. During your transition from SPM to college, or college to university, you will have a lot of 'downtime' where you need to study for exams/assignments and can't play as much.

Being a dps class you can afford to slack a little. Don't even think of playing a tank, it takes wayyy too much time when you hit 70 and start to gear up. The time, effort and tanking pressure will compel you to quit the game... and that really sucks after putting so much hard work in it.

So roll a hunter today.