I have 4 days/3 nights to spend and I can't decide how to split them between Amsterdam, Bruges and Brussels. We'll be taking the train from Paris to Amsterdam and figured we might as well check out Brussels while we're passing through, but we've heard that Bruges is so nice. Is it worth spending any time in Brussels or should we just hit Bruges and Amsterdam? If you had 3 nights, how would you spend them between these 3 cities?

It's not worth spending time in Brussels

Brussels isn't that great - especially if you're limited for time. It is basically an area around the Main Square, which is pretty and a street of restaurants - which ain't that great. The rest of it is a commercial city, banks etc.

That's not to say it doesn't have it's plus points, but they aren't sufficiently plus to out weigh less time in Bruges or Hamster-jam.

Plus it's the home of all that's evil - the EU. (Nice beer and chocolate though)

If I had 3 nights and had never been to Amsterdam I would spend 3 nights there. Brugge is pretty; perhaps spend a day there if you want to.

I also would say that with such few days, I'd skip Brussels and go to Brugge instead. I was just in both cities in October and I'm glad I went to Brussels, but I'd kick myself if I'd miss Brugge. I'm almost done with writing my trip report which includes Brugge and Brussels if you want to read more about each city and my impressions. Here's the link to the trip report:
http://www.fodors.com/forums/threads...p;tid=34713441

Definitely Bruges and Amsterdam. If you want to make a quick stop at Brussels while passing through you can visit the main square, eat some chocolate and be on your way but the other two cities are more interesting. I have been to all three and would spend two nights in Amsterdam and one in Bruges. Most of the tourists leave Bruges in early evening so you can have a nice stoll and dinner without the throngs. There isn't much else to do there at night. Now Amsterday is quite lively and two nights would be worthwhile even if you just visit the red-light district one night and go for a nice dinner and comedy show at Boom Chicago the next night, for example.

David, there is MUCH, MUCH more to Brussels than the Grand'Place, the restaurant street (which is merely a tourist trap), the banks, commercial buildings and EU. You are describing a very superficial view of the city; I might have thought that too at one time, but living there for several years showed me how much more there is to the city than the hit and run tourist experience. I have posted several suggestions about the attractive, nontouristy, non EU parts of Brussels. We were back at our apartment there earlier this month and I found plenty of interesting things to see and do, as well as excellent restaurants (the details of which I have posted on Fodors as well--there is simply NO reason to confine oneself to the area around the GP).
However, with only 3 nights, trying to do Bruges AND Amsterdam will be a challenge, much less tossing Brussels into the picture.
Bruges is best enjoyed if you can spend the night and walk around before or after the daytrippers arrive en masse.

aconnell is traveling in March (from another post) and I doubt that there will be 'tourists en masse' at that time.. just saying that because we went for an afternoon one October and there were no crowds, no lines, 100's of empty café chairs on the square...