Swan Song is definitely his best, IMO. That said, I also have a soft spot for Wolf's Hour - a werewolf working as a spy and fighting Nazis during WWII is a recipe for awesome.
Have you read The Wolf's Hour by McCammon? That is, IMO, one of his two or three best. A werewolf who grows up to be a fricking SPY for the Allied Intelligence in WWII. But it's also a really hard-core werewolf story, with a great buildup and wonderful characters.
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You can also try Let the Right One In. Slow burn, but VERY good.
I am Legend by Matheson, of course, is one of the gold standards - and the science holds up remarkably well 50 years later (the guy was a genius).
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I absolutely DEVOURED The Passage trilogy.
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The Keep by F. Paul Wilson - not a "traditional" vampire, but an AMAZING story that eventually circles around and touches with Wilson's Repairman Jack series (also excellent!)
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Another McCammon: They Thirst
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Some others:
A Discovery of Witches (Harkness)
Children of the Night (Simmons)
Abraham Lincoln: Vampire Hunter (some good dumb fun)
Cycle of the Werewolf (King)
Cabal (Barker)
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Hope this helps!