I'd like recommendations as to the best airport to which to fly from the US in order to get to Trier and what is the best mode to get from that airport to Trier (e.g., train, bus, shuttle). Many thanks
The U. S. is a pretty big place. How about a clue for a departure point?
Philadelphia or New York
You are right that this is difficult. Since you didn't mention "car" in your list, we have to assume that is out of the question, and that you have no interest in visiting somewhere along the way, like the Moselle Valley, Belgium, or Luxembourg. Unless you have a family wedding or something in Trier, please don't expect it to have the stature of Brussels, Cologne, or even Luxembourg City. Trier is an important place to visit, it's not a "destination." (Opinion.)
I think Luxembourg City and Cologne are two of the best options to pick up a train. Second or third choice is Frankfurt, partly because it is served by so many airlines. When we flew to Cologne, for three terrific nights there, United added a Lufthansa connection with the regular website purchase for less than $100 per person extra. Because we wanted to see Cologne, it worked out great for us.
Here are two useful Rick links:
Since it's a gateway hub, Frankfurt would be your best airport. You can take the train from the airport to Trier in under three hours with one connection in Koblenz. See the timetables on the bahn.de (German Rail) site. Enter Frankfurt(M) Flughafen as your departure point. Koeln (Cologne) to Trier would take just as long.
You are apt to find reasonably priced non stops to Frankfurt from either PHL or EWR. There are frequent trains from the airport to Trier, usually requiring only one change at Koblenz in under 3 hours.