Day trip from Delpt - Gouda, Leiden or Haarlem?

Do you mean Delft??
If so, visit Leiden.

We are in Delpt for 3 days and looking for best way to spend a day trip.

Assuming you mean Delft, you have a ton of options, but you also need to flesh out your general plan for us so you can get better feedback.

IOW - are you solely in Delft and for 3 days total - and NOT seeing & staying in other places in the Netherlands? Or are you adding Delft as a second (or third...) home base after somewhere like Amsterdam or Utrecht or nearby Belgium cities?

It would definitely make a difference in my suggestions knowing what else you may be seeing and doing while there. To me, any of those places will be a nice time, so you're not at risk of a "bad" choice. Besides your trip's "when" & "where", I'd also ask "what are your interests" and what do you like to see and do on this kind of vacation?

Everyone will have a different opinion on this, but I loved Leiden; much more than Haarlem. I have not been to Gouda, but I would still probably vote for Leiden.

It's a beautiful university town and the home of Leiden University, which is one of the oldest universities in the country. Leiden has a wonderful atmosphere, too, with charming cobblestone streets and 17th century gabled houses. It has many historic buildings but does not have the "touristy" feel of many other places. It's a much more livable feel. The city has many picturesque canals and waterways, which are lovely to walk along and there are boat tours you can take. And there are lots of parks, gardens, and green spaces in Leiden.

Another vote for Leiden. I was pleasantly surprised by how much I enjoyed my day trip there from Delft in 2023.

Are you aware you can just use your credit card to tap and pay for all public transportation in the Netherlands? No need to buy tickets. It really makes getting around super easy.

Have a great trip!!

Thanks for all the advice. We are in Delft before a 7 day cruise. We planned to use Delft as home base. If we only have a few hours in Leiden, what would be the best to do?

If you only can spent a few hours, what are your interests? There is a wide range of museums (anthropological, archaeological, municipal, natural history, Pilgrim Fathers, windmill), parks (including the university hortus botanicus) and 17th century gables along canals.

janohara25, here is a link to a mini trip report from one of the regular posters here. She and her husband spent 4 days in Leiden, but saw a lot. So you might want to look through there to see what captures your interest. https://community.ricksteves.com/travel-forum/trip-reports/one-more-mini-trip-report-four-days-in-leiden-and-one-night-at-a-schiphol-hotel

For a day trip to Leiden, wander the canals and lanes of the university section of town. It's charming with lots of nice shops and restaurants to stop in and lovely canals (not as dramatic as Amsterdam's canals but they are certainly going to be quieter for the most part). Check out the Burcht which has a circle fortress with a lovely view of the city and of the Hooglandse Kerk (lovely church). There's also a little windmill museum called the Molen de Valk. All of this is within easy walking distance of the train station if you're coming to town that way.

There are several other museums of note too (e.g., American Pilgrim Museum, some art and science museums), but we did not visit those so perhaps someone else can comment on anything worth seeing in a short visit.

We stayed in Leiden for 3 nights last summer and found there's lots to see and do - well worth a visit.

There are several museums in Leiden, including the Rijksmuseum van Oudheden (National Museum of Antiquities), which has a wonderful collection of Egyptian artifacts. There is the Museum De Lakenhal (Municipal Museum), and the Naturalis Biodiversity Center. The Hortus Botanicus (botanical garden), which was established in 1590, was the site of the planting of Holland’s first tulip bulbs in 1593. Rembrandt was born in Leiden, and Albert Einstein taught at Leiden University. St. Pieterskerk is quite historic and worth seeing, even if you just check out the outside of it. Rembrandt's parents were married and buried there.

In addition, there are some nice themed walks you can take, like the Pilgrim's walk, Rembrandt's route, and so on. https://www.visitleiden.nl/en/culture/city-walks

We are really only in delft for 2 full days before heading to Amsterdam and the river cruise. Would we be better off staying just spending the days exploring delft? All your suggestions are appreciated

Delft is small. When I stayed there, I got up early, spent the morning in Delft, then did my day trips later morning. And then I had the evenings to spend back in Delft.

This is nothing you have to decide now. Have a couple of day trips planned and make a decision once you are there.