It's not the army that will win you games. It's your skill. This game is 15% luck, 5% army list, and 80% player skill. Give the best army list to the worst player, and the worst army list to the best player and the best player will always win.
There is a "Warmachine Primer" printed on page five of the rulebook (Hordes has one too). It says play your best game and don't be a Dbag. Yes, there is an official rule in the main rulebook that says that. Lot's of people forget that, or misinterpret it, or whatever.
Play the army you want, don't be a Dbag, and no one will ever say anything at all about you winning. But I caution you: There is not a "netlist" in the entire game that will enable you to win right off the bat as a new player. You will lose, a lot. If you win, it will be because of a fluke, the fickle hand of Lady Luck, or you are playing someone less experienced then you are. After about 20-30 games, you'll start to "get it" and then the real fun begins.
To become a better player in Warmachine/Hordes means to play against the best players in your area, ask them questions, and learn from them. Be gracious when you lose, and humble when you win. If you don't learn something from every game you play, you are playing wrong.
Good luck, and welcome to the machine... the WARMACHINE.