Ribs: Don't let sit or even hot hold too long if possible. They're best served pretty soon after pulling off the smoke (IMO).
Pork: wrap tightly in foil and hold for HOURS in a warm cooler, cambro or oven. They're pretty hard to screw up, but when they DO overcook, the meat texture gets a little mushy and soft. Not entirely BAD, but just so you know. I've seen a large coffin cooler full of pork butts hold temp for 10-12 hours.
Brisket: put some beef broth in the foil if you'r gonna hold it for a while to keep from drying out. I don't have as much luck holding these as butts, but then I've not done as many of them as butts. The longer the hold time, the more overcooked they seem to get, or even if they start cooling off....they're not as good as when they're nice and hot. Rest, yes. Hold, not as well.
These are, at least, my own personal experiences.
Big JT's Smokin' BBQ Competition Team
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