What is the best antihistamine to take for urticaria?

Depends: Most people respond best to zyrtec or xyzal, (levocetirizine) as long as they don't get drowsy with them. Everybody reacts differently to different antihistamines, though; most people with urticaria will try many of the available antihistamines, alone or in combination, under a physician's supervision, to get the best control of their hives.

Cetirizine (Zyrtec): In scientific trials Cetirizine has been shown to be the most effective 2nd generation/minimally sedating antihistamine. A 10 mg tab once a day is about as effective as Hydroxyzine (atarax) or diphenhydramne (benadryl) 3 times per day with minimal if any sedation. Sometimes higher Cetirizine doses or the addition of an h2-antihistamine, under an allergist's supervision, may be needed for control.