If you want play Poker seriously you should learn them in the following order:

Start with Texas Hold'em and learn it as best as you can. After 3-6 months you will know if this is your game or if holding more cards would be more appealing. If you must move, move to Omaha, (Pineapple is just for fun not for learning). Omaha will actually help your Hold'em game because it's similar to Hold'em with much more caution. With four cards per player the possibilities of straights, flushes, and full houses increase greatly so you can't be as aggressive and definitely can't bluff as much since most of the time someone will have a good hand. However, you will notice that the patience and the caution you gain from this game will have made you a more well rounded Hold'em player if and when you switch back. If you need to ask which one should only just stick with Hold'em. Card players who only play Omaha made that permanent switch as established players without asking. You will know.

If you don't like sharing cards on the table at all, then move over to Seven Card Stud. This is less simple than Hold'em but you may like looking at the other players face up cards and making a decision rather than sharing the cards. There are more cards dealt and more bet sessions in this game than any other so make sure you don't start playing this as a cold beginner.

Five card draw should never be forgotten since that's how poker began but casinos don't have tables with it. There are too few bet sessions so the casino's rake is too small and unprofitable. There is no "Flop" play, "Turn" play, or "River" play.....so everyone can play. You will find few questions and answers or discussions about this game in poker magazines because of it's simple form. I have yet to ever see a Five Card Draw tournament anywhere, however it does have it's own world of high skill level when played for very high stakes.

The High-Low games seem simple but require very high levels of skill so don't ever start out your poker learning with these games, save these for after you have learned all the rest.