i'd want the torpedo launcher. force the world into peace (maybe with me as dictator). then again i'd just get assasinated and it would get stolen.
i'd want the replicator, but where am i gonna get the energy it needs to make all that stuff?
the cloaking device would be nice (assuming it could be a 'personal' cloaking device), but that would lead me to a life of crime.
the holodeck would be nice, but i think it would get old prety fast. i dont like the idea of VR very much, remember that episode with Moriarty where they didnt know if they were still inside or not.
so my final choise is:
Teleporter
before anyone knows i have one:
teleport some cash from a bank vault.
the 'magic' i could do would get me all the groopies i could ever want.
once the world knows i have one:
convert a chair into pure energy and you can power the world for a month, lol.
i could monopolize the travel industry.

can you say "instant organ transplant"?
hell i could even go into crime fighting - "you come in and i'll shoot all of them......NOOOOO where did they all go?"