Q. Which one of these two bikes should I pick, Bullet 350 or Pulsar 220F? Needs: 1. Comfortable for rider with lower back pain, 2. Less Service cost and better mileage, 3. Long term reliability, 4. Better built, 5.Comfortable for side sitting pillion.?

As per your requirements, we'd suggest you to opt for the Royal Enfield Bullet 350. The bike offers a more upright seating posture compared to the sporty stance offered by the Pulsar 220F. It is also the most affordable Royal Enfield motorcycle and it shows how the brand has managed to keep this bare-basic roadster alive even in the BS6 era. For a better understanding of compatibility and riding comfort, we would suggest you to take a test ride. Follow the link and select your desired city for dealership details.

If you have lower back pain so it is my request please drop the idea to buy a bike, better you took activa or similar for above said all parameters

None of the above. Bullet are high maintenance bikes while pulsar are of bad quality build.