Not a decision we can make for you. All are nice places and worth visiting.
maybe my triplist can help you decide...
More help might be more forthcoming with more details.
What do you like to do? What are your interests? Are you traveling with children? (If yes, what ages.) By car? Public transport only? Time of year? Mid-week or weekend?
We are traveling by car, no children: 10 adults. We are into sightseeing interesting places. Maybe nice restaurant. But not shopping, bars, etc.
By car, with that many people, I'd say definitely skip The Hague. It has it's charms, but not over Delft or Haarlem, if you must make a choice for how to use limited time. Plus driving/parking will be much more of a challenge in The Hague and it's not as easily walkable as the other two. (I live in The Hague at present.) In Haarleem or Delft, you can drive to the city, park the car and then do most of your sightseeing on foot. If you do go to Delft, be aware that the construction around the train station is still going on and is still effecting the traffic and parking in that area.
i drove in the hague once..i was a nervous wreck..and i was with one person, not 10. haarlem and delft would be my choices
I would give Haarlem a full day. Delft at the very minimum 1/2 day. And would give The Hague a miss. If you intend to try seeing all 3 in 1 day, I suggest that you remain in Amsterdam instead and buy postcards of the 3 cities, because that's about what you would have time to see (a few monuments, a church and the market place in each city), taking in account transportation time on top of it.