They both have their own charm. For total offloading experience I would recommend Spiti.
But for airless comfort of roads, and facilities Ladakh it is. But let's be clear, both are stunning
Ladakh and spiti are picturesque places with an edge for spiti over ladakh i must say go to spiti and just see the star density that place has and the eye alluring scenery is icing to the cake.
Dear Shantanu, there are other many places in Ladakh & Spiti. Just read below. (i) Leh
1. Hall of Fame Museum 2. Namgyal Tsemo Monastery 3. Leh Palace 4. Zorawar Fort 5. Shanti Stupa ( Buddhist temple ) 6. Shey Palace ( Monastery ) 7. Thiksey ( Monastery ) 8. Hemis Gompa 9. Magnetic Hill 10. Gurudwara Pathar Sahib 11. Khardung La (ii) Nubra Valley
1. Diskit Gompa 2. Hunder Sand Dunes with Camel Safari 3. Turtuk Village 4. Tiger Camp 5. Charasa 6. Ensa Monastery (Gompa) 7. Yarab Tso Lake 8. Panamik Hot Spring (iii) Pangong Lake (iv) Changthang
1. Chushul 2. Hanle with Indian Astronomical Observatory 3. Tso Moriri Lake with wildlife 4. Puga Valley 5. Tso Kar Lake 6. Yaye Tso 7. Chumathang Hot Spring 8. Kiyari war memorial (v) Aryan Valley (vi) Leh to Kargil
1. Nimu village 2. Likir, Alchi, Lamayuru Monastery 3. Fotu La, Namika La 4. Mulbekh Monastery (vii) Suru Valley
1. Parkachik Glacier 2. Nun Kun mountain 3. Rangdum (viii) Zanskar Valley
1. Padum 2. Phuktal Gompa 3. Chadar Trek (ix) Hemis National Park
1. Stok kangri 2. National Park but Main Focus SNOW LEOPARD (x) Leh - Manali Road Trip
*** Leh --> Shey --> Thiksey --> Karu --> Upshi --> Rumtse --> Taglang La --> Debring --> More plains --> Pang --> Lachalung La --> Sarchu --> Suraj Tal --> Baralacha La --> Zing Zing Bar --> Darcha --> Jispa --> Kyelang --> Gondhla --> Khoksar --> Rohtang La --> Kothi --> Manali