StLo as American, there is a large number of AI platoons, so you can move up in support of them.

Toum as German is easy if you are observant and not concerned with the bonus goals. But, be aware that killing infantry that are prone in a building are tough to kill. That's ment to simulate the infantry platoon taking cover. Wait from them to move or use lots of 75mm HE to pulverise the ground they are laying on. If they are a bazooka team, don't wait for them to start moving.

Toum as American is good if you have all M4s and have a little understanding of wingman control. It starts as finding a hull down ambush position, morphs into a counter attack, and ends with a dash to reinforce a different area.

Easiest campaigns are Desert as German and Normandy as American. Desert as American is not too bad once you learn how to deal with the few Tigers you run across and you have enough M4s for the entire platoon. Normandy as German needs good aim or lots of ammo. Italy has some one sided battles for both sides.

Another tip while learning is to set the game map to show all units (options button, then realism panel). I would change that back to showing only spotted units as soon as possible. Some of the fun is not knowing exactly where everyone is.

After you have tried vanilla PE for a bit, Michael Y has a code mod for PESE 1.2 called Full Monty
http://home.comcast.net/~pedg_library/MY/PE.htm

I suggest you try both vanilla PESE1.2 and Full Monty a bit before PEx, PP2x, or PE3.