Thank you, that makes sense, I just had tickets I had picked out from united airlines that were going through Paris but I haven't got the tickets yet, I did see that American Airlines have flights going to stop in London first, deciding which route is better.
Thanks for your reply on this :)

I have my US passport, I checked and says no Visa required when staying for less than 90 days

In fact I do use T-Mobile as my carrier, I'll have to check on that.

Just want to say thanks everyone that took the time to reply with answers on all this.

Have fun, and please report back to tell us how it went.

Just one more question, promise :), I am about to get my plane tickets and first I look, I was going to book one that is going to Paris first. I also see options to stop in London and one that stops in Frankfurt before going to Luxembourg, which would be the better route to take?

Are the routes all on the same ticket? I'm assuming they are. How are the connection times?

All three airports are very busy. Airlines tend to, imho, under estimate airport transit if there are terminal changes and passport control.

At the minimum, I prefer at least 2 hours in any of them, but would prefer a bit longer if possible.

Yes, all on the same ticket, some are an 1 hour and 30 minutes, but I do understand that isn't enough time, think I saw a few for 3 hours, I'll keep that in mind.

I assume you are flying American on your first leg. I am also going to assume this is all on one ticket? If so connecting in LHR you will probably flying BA. I don't fly American much so I do not know what airlines will take you from CDG or FRA. If the costs are the same your choice should depend on time of departure from your home airport and connection times.
You don't want too short of a connection time or too long of a connection time. I generally prefer 2-3 hours. I am personally ambivalent about your choices of connecting airports. Are you checking a bag? What time you land at your destination may also be an issue.

Like Travel_Nerd, I want at least 2 hours between flights and I want all legs of my journey on the same ticket. And like mjs, I consider actual times for departing my "home" airport and reaching my planned destination.

I'm sorry I've lost track of your itinerary, but FWIW, I would encourage you to consider not just the financial cost of your flights, but also the cost in time and energy. And it isn't just the extra time you might need for the stop: I once chose to fly into a city that wasn't actually part of my plan, but which had hourly train connections to my intended destination and cost less than 2/3 of what it would have cost to fly into my planned starting point. Good deal, I thought! WRONG. There was a problem with the train lines, so instead of hopping onto the next train, it took me more than 12 hours to get a train. And by the time I recognized the problem, it was already too late to cancel the first night of my lodging in the planned destination, so I had to eat that cost AND pay for a place to stay that night, and trust me, last minute lodging can be pricey. Lesson learned!

P.S. Ask your questions! No need to apologize. :)

90 minute connection time is possible. But it makes things tight if there are any delays. Having a longer connection helps absorb delays.

Given that this is your first international trip, I'd give yourself a longer connection. So you can get through logistics, find a loo, get water or snacks if you want them, and breathe a bit before your connecting flight.

Hi Starman32,

I'd go for Frankfurt or Paris. In a pinch, if something happens to your onward flight, you can always take a train from Frankfurt or Paris to Luxembourg. Paris to Luxembourg is about 3h30 or 4h30 with 1 change, and Frankfurt to Luxembourg is about 4h30 with 1 change.

You can check train schedules at

www.bahn.com

Have fun as you plan!
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I take it you are connecting in Chicago so this is a two stop itinerary? I would think United would have more flight options than American. You are going to be exhausted by the time you reach your final destination. Other things you might consider are on time histories of your possible flights, available seats.