I will be traveling with my father in May and wondering best way to get to Cologne, he has relatives he has never met. Would it be better to fly into Amsterdam or Frankfurt, also, would it be better to drive or take the train? I have driven in Germany before but not in a few years.
From either airport, I'd just take the train since you are going straight there. German trains are extremely efficient.
Check out Duesseldorf airport, which has flights direct from N.A., sometimes a bit cheaper and certainly a lot closer. There is a train station at the airport and its about 40 minutes to Cologne.
Flights to Amsterdam and Frankfurt are usually some of the cheapest from US. Train from Frankfurt airport to Cologne is about 1-1/2 hrs, from Amsterdam airport to Cologne closer to 3 hrs. I personally would fly into Frankfurt and take the train to Cologne. As far as train vs. car it depends a lot on where else you will be traveling and will you want a car for other places you are going. Dusseldorf is the closest of the three but from what I've seen flights from the US are more expensive to there.
You can take the high speed ICE from FRA to Köln in less than an hour, but the standard fare is 134€ ($145) per person. You can get advance purchase tickets starting at 29€, but that's a popular route and the lowest priced tickets sell out quickly. I don't see any for less than about 65€, even 3 months in advance. And those tickets are train specific and almost non-refundable on the day of arrival, so if your flight is late .... However, the route taken by the high speed train is unremarkable. For 52€ ($57 total, $28 each), you can get a Quer-durchs-Land-Ticket and take regional trains on the route that goes along the Rhein gorge (through Bacharach and St. Goar to Koblenz, change in Koblenz to Köln. The QdL-Ticket is always available at that price just before travel time.
I would not think about getting in a car and driving immediately after arriving on an overnight, trans-Atlantic flight.
The Frankfurt to Cologne ICE route is one of the fastest sections of the entire German rail network. If you fly into Frankfurt, you can catch the train directly from the airport. Trains leave hourly.
Thank you for all the advise, which is why I love this sight! One mor question, any suggestions for a great brewery near Cologne?
The local beer in Cologne is Koelsch, actually a light ale. Tradition dictates 200 ml (about 7 oz) cylindrical glasses, but 300 ml glasses are available and even 500 ml (Tourist!).
Here are some of the breweries: http://www.cologne.de/eat-and-drink/breweries.html
My favorite spot is Papa Joe's Bier Salon in the altstadt. Amazing collection of working coin op music machines, plus his own "Tuenis and Schael" automaton with the play list and coin box on one of the room pillars.