Kyrgyzstan or Tajikistan

Hi - I'm planning a Silk Road trip. We'll be coming from Kashgar and finishing with the big cities in Uzbekistan. We will have about three weeks for Tajikistan/Kyrgyzstan. We would like to do some good hiking, lakes etc. My sense is that Kyrgyzstan is more accessible etc but that the Pamirs etc might be more spectacular. So I'm interested in getting opinions in which way is best (we'll be travelling the whole way by land so I don't think it's possible to go to both). Thanks!