I think Crowder would complement well with any of the above. Channing has a good feel for slamming himself into the hole in order to force the running back where the defense wants instead of allowing the running back the ability to choose where he wants to go. That would work well with McClain, who is more used to being able to flow to the runner and not worry as much about that kind of gap control. It would also work well with Weatherspoon, because right now Spoon doesn't know how to do that AT ALL, and so if you put Crowder in there next to Spoon you have at least one guy that knows how to do that while the other guy is more of a freelancer that attacks the ball whichever way he can and at the same time is a good coverage backer. I think that Crowder and Dansby are both such smart and experienced veterans that they would complement each other naturally.
Crowder and Spikes are a little harder to tell. I say that simply because they both have that great feel for slamming the door on the hole and playing gap control, rather than freelancing to the ball or having the defense built to channel the ball toward them. Also, Spikes is a zone cover guy that thrives on reading the QB's eyes. He's not been given as much straight up man coverage in his days at Florida, which would mean that Channing would have to continue being the stronger cover player. There is some thought that if you have these two working the interior then you need at least one stronger cover guy amongst the OLBs...or maybe both. Of course, there is something to be said for that. Denver had Mario Haggan at the strong side spot, and Green Bay had Clay Matthews, both I would say had more versatility coverage-wise than Matt Roth, Jason Taylor or Joey Porter. Manny Lawson's athletic ability came in handy that way in San Francisco.
But anyway, I don't think there's one way to skin a cat in this regard. Crowder's a good player whom I feel takes a beating because he's not a fantastic player. Akin Ayodele and Reggie Torbor are the guys who struggle too often to achieve "mediocre" status. I would start there.