We will be four people, and we are trying to decide how to spend our time and money. Having some form of a car will give us more freedom with our journeys, but is it more economical to rent a car, or get a private guide tour?
It all depends what daytrips you had in mind. A warning, though, that the highways in North and South Holland are some of the most congested in the world. Check to make sure you can't use public transportation to reach your destinations. Otherwise, be prepared to spend hours in traffic.
I would utilize the public transport. I don't know how much more freedom you could want than the Dutch train and bus system. In living here we have been able to see everything we could imagine and have never gotten in car. If you know where you would like to go I would be happy to help you find the easiest routes.
Driving a car in Holland can be challenging, and inefficient. Especially in a country that has about the best overall train system in Europe.
Trains are frequent, cheap, and go just about everywhere. A car would most likely be less economical. Fuel stations are few and far between And parking can be a BEAR, not to mention pricey.
Most Dutch cities are small enough that the train station is right in the mix of everything: Just hop off, and explore. And there is no need for a car, most are so walkable.
If a train doesn't go there, efficient trams, or buses do.
I'd forego a car entirely. Use that time on the train enjoying the sites, and save some money.
For Delft, Liden, Haarlem, Rotterdam, etc, train is they way to go. Cheers.