I'm fairly sure that no matter what format you play, the main goal is winning/increasing your bankroll.
^ That stated, what experience do you have in regards to Poker in general?
Then dissect the different formats to see what suits your Poker habits the most.
I personally prefer playing MTT's,
but those aren't really ideal for building a quick bankroll.. You kinda need a decent roll to start with MTT's as you can have a bad run losing quite a few Buy-In's.
Not being rolled for the format you play can get you in trouble, fast.
EDIT: Note; Freerolls
(especially the CC ones), are a good start if you don't really have a BR, or if you have a small BR and want to give it a little boost.