I think I should expand on my snarky comment from before:
I am one of the people who think Mayo is overrated. It could just be because he has played in a bad defense for a few years, but I've never seen him as a game changer. I have a suspicion that his career may end up being reminiscent of London Fletcher: a guy who is pretty solid, racks up a lot of tackles, but not a guy who the offense has to design a game plan around.
I actually think Spikes is really underrated for just how devastating he is between the tackles, but he is useless in coverage. It is painful to watch him stagger after TEs and backs in the flats.
I think Hightower has the chance to be the best of all our linebackers, if he continues to develop. He is more athletic than Spikes, while retaining Spikes' high motor and intensity.
If Collins can be the sub-package coverage guy that we all hope he can be, to cover up Spikes' liabilities in that area, then we shall see.
(Of course this is all for nothing if the secondary is continued to be made of four slices of buttered toast, and the line can't get a pass rush)