If you are just starting out, I would suggest starting with Standard for constructed or Sealed for limited: while I prefer Modern and Legacy, the entry fee of a new deck can be pretty daunting. Start by researching the standard metagame, proxy decks and playtest them (as in they wont be tournament legal) prior to buying one that suits you. Sealed helps here as the cards you pull can be put into standard decks and it isn't as knowledge heavy as draft can be.