My suggestion, first off, is to send them on infiltration and sudden strike missions. Think Special Forces. It's what they're good at.
Minions are going to harass them a lot, because it doesn't matter how much damage they do, minions die from a hit. So use minions with care (Unless you want to really scare them).
Skirmishers might offer some interesting play, because they're as mobile as your PCs by nature. Problem is, with fast PCs, they will run those fast guys down and feed them steel.
Artillery and Controller monsters are very interesting. They, like Strikers, are glass cannons. It results in a very "Fire fight" type situation where the PCs are ducking behind cover to fire back, or trying to get in the artillery's face. Giving these guys elevation or cover behind a wall of muscle would be an interesting challenge.
Brutes are scary, because they will certainly put the pain on your strikers. However, I think Soldiers are very good, because they shut down mobility. Strikers, all about the mobility, will have to deal very cautiously with Soldiers. Also, Soldiers have higher AC and Defenses, making them a good foil for your strikers.
I would suggest to actually mix your battles up, and see how they play out with your PCs. Give your players an escape route if they are real low, or the enemy doesn't make a habit of killing foes (hostage rescue?).
I do think that a fight with two beefy soldiers and then some lurkers might actually scare your players (namely because Lurkers can bring the hurt).