My personal opinion is that hire cars are a waste of time in a part of Holland where the distances are small and the train services immaculate. I travelled down to Delft a fortnight ago, the service was absolutely on time: First class is much better priced than we're used to, and I think worth having. You can check and print out the timetables you need, the relevant fares and even how to use the ticket machines from the Dutch railway website, in English.
And in Amsterdam, all the trams start at the station, so it's not very easy to get lost!