For practical use, I'd probably pick Teleport or Transform.
If everyone could Teleport, much of the global pollution problem could probably be solved (or, at least, mitigated).
With Transform, cosplay will probably get a lot more interesting...
In fact, you'd probably trigger massive RFS (Rabid Fangirl Syndrome) at an anime convention if you walked in while Transformed as Cloud Strife, any of the Kingdom Hearts characters, a Pikachu (imagine the squeals), a life-size Pikmin (if you survive long enough, imagine the even bigger squeals), Marf, etc., etc. XD
With Transform, you could also:
1) pull of the greatest identity theft scams the world has ever seen
2) become the greatest spy the world has ever seen
3) run plastic surgery out of business
4) never get caught with anything
5) freak people out by going around looking like a dead person
6) Win Mr. Olympia/Ms. Universe (does the competitor next to you have bigger pecs/boobs? *insert Zelda-Sheik transformation music* Problem solved.)
7) Win Hide n' Go Seek. Every time.
8) Confuse thirsty people who are lost in the desert by Transforming into a vending machine and running away from them when they get too close.
9) Are you an exile of your native country? Wanna return and start that coup d'etat you've always wanted to start AND avoid political imprisonment but were too afraid and/or recognizable to do so? Well, then the Transform-O-Matic TM is just the product for you! With this amazing product, all of your problems will be solved! Call now and receive a SECOND Transform-O-Matic TM all for the price of ONE! Hurry! This deal will only last for a limited time, so call now!
...XD.