I think it largely depends on what you are interested in.
You could also go the other direction and see Paris.
If you wanted to see Benelux, I would do the following:
Day 1: Brussels
Day 2 & 3: Bruges - do the bike ride to Damme or Sluis
Day 4: travel to Delft, stopping in Gent along the way; Delft is a college town but is also a beautiful Dutch town. There is a wonderful square that is surrounded on all sides with cafes and restaurants - a lovely way to pass an evening
Day 5: Delft - even better if it is a Thursday or a Saturday and the market is town; there is also the porcelain factory, old churches (including the burial site of the House of Orange), a Vermeer museum, beautiful botanical gardens, lovely canals...
Day 6: Kuekenhof to see the tulips in bloom; you can take a bike ride from Leiden and travel through other flower fields on the way to the gardens or else there are direct buses from Leiden, Haarlem, and Amsterdam. Biking would take you through several smaller towns in addition to the flower fields. You can sleep in Leiden or go ahead on to Amsterdam.
Day 7 - 10: Amsterdam with possible side trips to Utrecht, Haarlem, or the Kinderdijk bike ride out of Gouda. The kinderdijk ride is one of my favorites; you get to see over 30 windmills along the way, take a ferry, bike through several small towns, pass farms with cheese shops, and see the beautiful landscape.