GK(D) - I've used both roles and had the same effectiveness. If you have a mobile keeper and your coaches think he can play as a sweeper, go for it.
Full Backs(D) - I like having my guys play as fullbacks instead of wingers. Even with more offensive threats, I find that the fullback setting gets the fullbacks forward enough, even on a defensive duty.
Central Defenders(D) - No surprise here. Again, I keep things simple with roles set to Central Defender. I don't want limited defenders or players that are best in that role. I want stud defenders, not limited ones.
Wide Midfielders(A) - I prefer the wide midfielder role instead of winger because I want my wing players getting more into the middle of the pitch when they run in from deep. The winger role tends to limit them to the edges of the pitch, which works well in my 4231 but not in this 442. I prefer attacking duty over support because I like the guys to do their attacking by dribbling at defenders and not relying so much on through balls and longshots (which is for the central midfielders).
Advanced Playmaker(A) - The sparkplug. With an advanced playmaker role and attacking duty, you need a stout playmaker here. The better your player here, the better the entire offense becomes. You want someone that takes control of the ball and dictates to the defense.
Central Midfielder(D) - The enforcer. He's the cover for the advanced playmaker. Even with a supreme player like Rodwell, I still prefer the central midfielder role over ball winning midfielder, which I think causes too much ball chasing. The central midfielder role restricts how big of an area the player closes down and helps maintain shape.
Trequartista(A) - The partner in crime. You might think having a trequart and an advanced playmaker is overkill. I beg to differ. While both do have maximum creative freedom, I don't find that to be an issue at all. If anything it gives you extra opportunities to attack. The trequart is made to just float around in the final third and wait for attacks to start. Once they do, he usually finds the ball and can start the final push toward goal. If another player initiates the final push, he'll be smart enough to make himself available for a quick pass and shot.
Poacher(A) - The closer. All he does is score goals. And set up the other attackers. I love using a poacher, and once you have the proper player you will too. Find someone quick on and off the ball and the battle is half won. The goal scoring will come.
Please note that this isn't a silver bullet tactic. Use this tactic to learn how your team plays on the pitch, and make subtle changes here and there to suit your needs. I've been using this tactic for 3 years now so I have the benefit of knowing the kind of players I want at all levels of play. The more you use a 'vanilla' tactic like this, the more you'll learn what tweaks need to be made. Good luck!