A common mistake when vacationing is rushing around trying to see too much. You spend all your time traveling instead of vacationing. There's a lot to see and experience in each place if you relax and take the time to do it. The more time you spend in one place the more comfortable it becomes. You get to know your way around, meet the locals, discover and experience the kinds of places that you would otherwise never even know existed.

Your schedule includes 6 days of traveling plus jet lag, that's almost half of your trip. I'd pick two places - in this case Paris and London - and make Paris the primary, branching out with day trips and maybe an overnighter (Ronchamp, paleolithic caves, etc.). Then finish in London <yawn> for 3 nights max unless you have something else to do there.

I like Miles' idea. You gotta go to Amsterdam too, not for contemporary architecture that much, but for the vibe of the city. Oh,  and yes, Berlin is a must, if you can. Brussels - meh.

I would cancel Brussels, Rotterdam, and London. Certainly Paris is a must for at least five or six days. I would go to Munich (you will be there for Oktoberfest and must see the Englisher Garden!), Prague, Vienna, and Florence. Any time left over I would try and schedule Barcelona, but that might be pushing it. You might want to see Prague OR Vienna and put the one you missed on your bucket list.

I don't know what your gf's reason is for wanting to go to London - to my mind it is the least nice place you can go in Europe and one of the most expensive. I'd take expensive coffee & sightseeing in Copenhagen over London any day. 

I'm biased for having lived in some of those places you mentioned - I would take 4ish days each in Copenhagen, Berlin, Amsterdam and Paris. From Amsterdam you can do a day trip or two to Rotterdam, Utrecht, Delft, or Haarlem. From Copenhagen you can easily take a day trip each to Helsingor up north, Roskilde to the west or across the bridge to Lund or Malmö. Berlin has enough to keep someone occupied for years (I recommend the bunker gallery, by private appointment only). 

I could recommend loads of things to do in each city... if you decide to visit any of those and want some restaurant/cafe/event/other recommendations send me a message :)

First things first...thank you for the comments/advice! 

To clarify, all travel between destinations will be by plane to maximize efficiency, unless a destination is close enough for a short train ride. What is now 17 days, its turning more into 18-20 now so there are possibilities to add more stops. 

I'm not sure how negotiable London is...but I tend to agree it's a bore. Having a free flat to stay in makes it's affordable at least. One positive is escaping to the south for a long overdue trip to see friends in Chichester. 

Last spring I took 13 days to travel to Berlin, Munich and Vienna. Absolutely loved Vienna which is why I want to go to Prague this time around. Munich/Bavaria was amazing, it will be hard to resist not going back for Oktoberfest. And Berlin...I was there for nearly half the trip so I saw pretty much everything I wanted to see, but I agree there's an infinite number of things to do there. Missed out on the Berghain(entertaining but long story), having another year to mature now that seems a little less appealing.

Brussels is on its way off the itinerary. Rotterdam/Amsterdam is definitely happening. My friend in Rotterdam insists she can show us more than enough in 2 days to leave architecturally satisfied. 

Prague is a lock, it's beautiful, I can't wait.

NYC > Amsterdam > Rotterdam (fly out AMS) > Prague > Paris > London (with Chichester) > Reality      

...sounds like a plan. Possibly add Copenhagen or Graz if I get more time.

I think a Europass on Eurorail would be the way to get around the continent, especially if you want to be able to change your plan as opportunities arise. Flying is such a hellish experience in the US, can't be that much better now in Euroland?

Eur-Rail  passes must be one of the biggest scams ever sold to North American tourists in Europe. Airfare can be cheaper from certain places; if not, booking a month or two in advance on tgv.fr or renfe.es or db.de is usually about 10 times cheaper then getting a restricted rail pass.

Flying in Europe is way easier than the US, and generally the complete opposite of a  hellish experience. If you fly luftansa, air berlin, SAS, Swiss, Air France, KLM, or one of the other 'non-discount' airlines, you will generally still get a free bag, free alcohol on board and sometimes even a butter-filled pretzel the size of your head.

Traveling is not just a short plane ride. It's decamping to the airport, security, waiting, flying, getting to your destination, setting up lodging. In other words it's pretty much a lost day.

The trains in Europe are great, very comfortable and a visual treat rolling through the countryside. If you're going to lose a day traveling, do it in style. Some of the most memorable parts of my travels have been on trains.

MJ, yes - was going to add a most train lines terminate in, or adjacent to, a city center whereas airports are more remote.  The added time for a train commute can easily be offset by the wildcard/hassle of transit (or expense of cabs) to the airport.

Also with trains (I'm discovering) if you book "locally" (as Stephanie suggests) you can look into scheduling a stopover of up to 48 hrs on the same ticket which can save some money.

I think (again - learning) Amsterdam - Prague, Amsterdam - Copenhagen, are candidates for a night train if you fancy that.  Efficient but not the most restful travel option...

No Italy??  No Rome?  No Florence?  No Venice?

Munich, Prague, and Vienna are wonderful but have a certain sameness about them to be included on the same trip, I think Florence would be a must, and maybe Barcelona if it could be worked in.

Travel by train, usually the scenery is great and the amount of time between cities isn't that much more than flying when you take into account getting to the airport, etc. DONT get a Eurail pass. It's a rip off. Just buy your train tickets in advance.

Brussels is tiny. If you must, do it in a day. There's plenty to do and see in London! (But hey, I live here). Granted, it doesn't really have that European feel that you might want for your European vacation. I would hit up Rotterdam and Amsterdam over 3 days. I can't comment on Prague. 4 days in Paris was plenty for me, but then, I felt like it didn't live up to the hype.

I highly recommend Barcelona, Rome, Florence and Venice.

for your 'past trip considerations', Wales, Scotland and Ireland are great if you want more of an outdoorsy time, outside of the cities they are the best. I felt Dublin was hugely over rated and Cardiff is literally a half day trip to see everything. Edinburgh, on the other hand, is lovely. And if you do end up in London I would suggest that you take a day trip out of the city to Bath.

Hello Lits, I agree with the lady about Paris and London, those two cities are a must, I suggest you to rent an apartment in Paris in order to get the best of your trip and spend some romantic moments out there, try http://www.city-getaway.com/en/apartments-to-rent-in-Paris/2 for the booking. Good Trip.