I've been a Roy Williams fan since his early days at Oklahoma. I would take Roy over any other safety in the league... not so much because I think he is THE BEST of them all, but I obviously am biased in my admiration for the player and THE MAN that Roy Williams is. He is nothing but class and is one of the few people in professional sports these days that I would not mind my kids looking at him as a role model (on and especially OFF the field).
That said, I have the utmost respect for Brian Dawkins. I haven't seen a lot of him other than highlights and such, but, if you look at his stats, he's an amazingly good Safety. Some people in this thread are labelling him as past his prime and on his decline... I can't argue that, but I think some would be surprised to know that, when Philly was struggling last season offensively and defensively, Brian Dawkins had the 2nd best year of his career STATISTICALLY.
I believe Dawkins was THE BEST safety in the league last season STATISTICALLY. He was very well rounded and led the big name safeties (Roy, Sean, Troy, Ed) in most every category.. INTS, FFs, Pass Defenses, and sacks. (I'm going from memory here so don't flame me if I'm wrong on 1 of those)
Obviously that doesn't just do away with the discussion of who was THE BEST because stats don't show everything. I wish they kept stats on TD's and receptions given up.
Bottom line.. I'd choose Roy if I had to choose... but, I agree with KC Joyner, Brian Dawkins is the best FS in the league and Roy Williams is the best SS in the league.