Hi Pratyaksha, I have just returned from Himachal Pradesh so I am going to be biased towards it and tell you to choose Himachal Pradesh for this trip. The scenery is gorgeous, the temperature is pleasant, the food is tasty and the people are extremely warm and friendly. However to take a more objective call on where you want to go, I recommend that you check out the following compilation pages:
1) Himachal Pradesh: https://www.tripoto.com/himachal-pradesh
2) Kashmir : https://www.tripoto.com/search?keywords=kashmir Hope this helps!