Wow great off-season thread, such a tough question!
Meth's hipchecks were a thing of beauty, he seriously had a few of them over his career here that were alltime poster-worthy. I remember being so pumped when he flipped Crosby like a lil' bitch. That was awesome.
But the a-train was a friggin wrecking ball. He and phillips were the best shutdown pairing we've ever had, and I think they were probably the best defensive pair in the league for a short time. Volchnkov would have had a longer career if he'd not been a shot-blocking machine and played all out all the time the way he did.
Meth was probably the better overall player though, especially because he and Karlsson had great chemistry and each understood their roles and how to play off each other. But I'd imagine there were others who could have done something similar paired with prime EK.
f*** it, I'd rather have the A-Train, dude was a non-stop beast. Pretty special player, especially these days. If we had that on our team now, everyone else would play 2 inches taller and 20 lbs heavier.