Well it's all about your preference. If you like the mountains you can head to Kashmir, Dalhousie, Dharamshala or somewhere in the North East like Sikkim or Cherrapunji.
My personal choice for a trip in April would be to the Andaman Islands. It's the best time for Scuba Diving and other water sports.
Manali,Shimla as they are worth your money and requires less time and are light on your pocket.we are arranging trips in himachal feel free to get more info @www.theparadisenorth.com Happy travels