I think UMF is better, but this year's already sold out I heard. If I'd go, I'd only go because it's Swedish House Mafia's last presentation, so it will be a pretty sick environment. My older brother (26) is going. My other brother (24) was going to go to Tomorrowland but decided to go to Amnesia in Ibiza.
It really depends. If you do drugs, then you're gonna have a blast- most drugs are very cheap and they are passed from hand to hand very easily. But if I were you, I'd totally go, Tomorrowland is definitely in the Top 3 EDM festivals in the whole world.