Good question. Alot of them would be very useful and very fun. I don't think I could pick one, but I'll tell you what I'd do with my favorites.
I would use Whirlwind Sprint to win Track Meets.
I would use Become Ethereal to jump off cliffs, etc.
I would use Unrelenting Force in hallways or streets crowded with people.
I would use Slow Time to get into Fist Fights.
I would go to an animal shelter and use Animal Alliegence.
I would Fire Breath/Ice Breath to subdue criminal.
I would use Detect Life when stealing cookies XD.
Almost every shout would have some use in the real world. svcks humans can't shout
