If you're going to school and plan to get a better job unrelated to UPS, go ahead and become a sup. They get an extra 5,000 in tuition reimbursement. But, it's much, much, much harder for sups to get a driving position. Everyone will hate you, but that's besides the point. You can also climb up the useless-
ladder and potentially make a lot more than drivers do (after a lifetime, prolly). Hell, you could even become the greatest
bag of them all.
If you want a driving position, learn how to drive a standard if you don't know already, then sign up for cover driving or Saturday air driving. It'll take something like 4-5 years, probably, maybe less, maybe more, but you'll be offered a full time position.
You will also not be protected by the union if you become a sup, obviously, because you become the enemy.