Delft vs. Haarlem

Delft. You would probably also have time head into nearby the Hague as well. Rick's Guidebook has more details on the Delft/Hague combo day trip.

http://wikitravel.org/en/Delft

http://wikitravel.org/en/Hague

I'll throw a third one into the mix, if that's OK....Utrecht. A wonderful huge market on Wednesdays and Saturdays at the entrance to the old part of the city (very close to the railway station), a wonderful old town to wander through, and a magnificent set of canals. The canals are much nicer than Amsterdams, IMO....they're down a level from the street, and many of the old storage warehouses at canal level are now restaurants and bars. About half an hour from Amsterdam by train.

On second thought, you could actually visit both Haarlem and Delft in a single day as well. Both places are on the same rail line, so there are direct trains connecting both places with departures multiple times an hour.

Both are nice, but if you have to choose...Delft...

I'll also give a vote for Utrecht as an even better option. It's just as pretty as Delft or Haarlem, but livelier than both. As a rail-junkie, I also really enjoyed the Nederlands Spoorwegmuseum (Dutch Railroad Museum), although non-Dutch speakers might find it a little less interesting.

Delft, Haarlem and then Leiden (which has a GREAT Saturday market and is convenient to the airport). Delft is really pretty and Haarlem has a great square.

another vote for Delft. Having stayed in Haarlem on a RS tour, and visited Delft on a separate trip, Delft is the one I want to go back and visit again.

This is a rare thing for me to do - but I'd say Delft over Haarlem. Much more to do there, many more things of historical interest, the pottery shops, etc. Even though my heart lies in Haarlem.

It also depends on what you like to do - if you like historical things, pottery, Delft for sure. If you like shopping, Haarlem is hard to beat, and it has a great square and cathedral.

But if I were chosing personally, Delft.

Delft, if you like Delftware and a nice town square city. But do consider Utrecht as mentioned above. Great resturants, shopping on the winding "old" canal are worth the trip. There is a great music museum with small musical clocks to large street organs, a guided tour in English was wonderful; National Museum van Speelklok tot Pierement.

Delft isn't just pretty pottery:) It's also Vermeer's hometown. Right in the city center is an excellent museum about his life and art:

http://www.vermeerdelft.nl