My typical loadout is 1 sniper, 1 shield, 2 assaults, 1 heavy, and 3 riflemen. Typically, I use the shield and 2 assault as forward scouts (since you really don't want just assault units scouting when you get to a crossroads or other likely ambush site). Or if I'm not really moving, shield in the rearguard paired with a rifle.
The real strength with the shield units is buying you time while being able to use all their TUs without being entirely exposed. One of my favorite tactics is spreading out my other units around an alien door, then sending in the shield to open the door, run in and scout the next room, then run back, shutting the door if necessary, before hunkering down behind their shield. And if they take reaction fire, oh well, they've got a shield anyway (though that's really rare with the incredibly slow pace I clear places at).
In other news, RIP, 3 high level soldiers, dead to an alien fighter squadron popping Charlie 1... Now I need a new sniper, shield, and assault. I may even have to resort to calling in Major "Cries A Lot," the soldier with 38 bravery (she started with 35), named for her first mission, where she panicked and fled 3 times in a row.
Though by far, my worst soldier was one in the Charlie 2 squad. He went berserk twice in one mission, shotgunning the sniper and shield to death. I was kind of happy when he died on the next mission. So uh, yeah, having a high bravery skill turns out to be pretty darned important...