Avoid first generation antihistamines like Benadryl (diphenhydramine) except for emergencies such as wasp stings for folks with allergies. Diphenhydramine and other early antihistamines in the anticholinergic family are associated with increased longterm risk of dementia and hallucinations.
In particular avoid Nyquil and similar all-in-one remedies. Those often contain two, three or more anticholinergics. Younger folks can usually get away with taking those but there's an increased risk for older folks. I've seen it in my family as a caregiver for my grandparents and mom.
I take only the original or reputable generic versions of Zyrtec, Allegra or Claritin. I'll switch around every few weeks if one doesn't seem to work as well. And I use nasal anti-inflammatories, asthma inhalers and pseudoephedrine for congestion. I'm allergic to all of Texas.