Manali is best, as you can enjoy Snow filled Rohtang pass, Atal tunnel, Solang Valley, Old manali, temles of hidimba mata nd vashisht temple with mall road of manali. Naggar castle
Shimla is the capital called as summer capital of Himachal. Filled with awesome peaks, valleys, mountains and hamlets it’s an ideal honeymoon spot. Right from Jakhoo temple to chail, Narkanda to annadale, Rothney castle to tattapani it’s one of the most sought after tourist spot. Manali nicknamed as lovers paradise is the Indian honeymoon capital. Filled with lot of adventure, cafés and peaks to view right from jogini falls to Parvati valley, Sethan valley to manu temple, Sissu to Bhrigu lake there is lots to explore. My choice would be Manali, though Shimla is 6 hours away.