Honestly I do see tons of physical potential in Rolondo McClain. He's very big and VERY strong. He also has good straight line speed.
On the other hand, Spikes is not quite as strong and not quite as big, though big and strong in his own right, and he has without question the better agility, motor and physicality.
Instincts and ability to read the ball and quarterback are up for debate. You know where I come out, I know where you come out.
The thing that gets me about this breakdown is, in the NFL...players get bigger and they get stronger. They don't necessarily get more agile and they don't necessarily get better motor, or more physical.
So while I agree that McClain is going to be pegged as the guy with more physical potential, I think that Spikes is the better player right now and with added strength, he could stay the better player.
And I also think that there isn't any question that while Spikes has the physicality and the comfort with blockers to play in the 3-4, Rolondo McClain is much better suited to a 4-3 Under like what Saban runs, which protects him better from blockers and funnels the ball to him, allowing him to use his size, strength, length and explosiveness to make a certain percentage of the "normal" plays turn into "big" plays.