Spring is definitely the season everybody should visit Amsterdam. From April 10-15 until the middle of May is the best period to see all the Magnolia Trees around the city, the Cherry Trees in Westerpark & the Tulip Fields at Keukenhof & Lisse.
You will never regret it, trust me! Just rent a bike, go around the city in this period, have a picnic in the park and you will fall in love!