Which is the best posture to Practice meditation?
Bhikkhus, the bhikkhu following the practice of my Teaching, having gone to the forest, or to the foot of a tree or to an empty, solitary place, sits down cross-legged, keeping his body erect, and sets up mindfulness, orienting it.
Then with entire mindfulness, he breathes in and with entire mindfulness he breathes out.
Maha-satipatthana Sutta

The above is the standard posture for meditation (i.e.: sit down cross-legged). Even though I can't remain in this posture for a long time due to back pain, I personally believe this is the best posture for meditation. Having said that there are many other postures suitable, depend on your situation (walking, sitting, etc.).