For pure relaxation, meditation yoga is hard to beat. Meditation yoga (also known as Sahaja Yoga) was developed by Sri Mataji Nirmala Devi, and aims to awaken a dormant energy, known as the Kundalini, which is located at the base of the spine.
Different practices have different techniques, for example Ashtanga is a far more physical process centred around heat and the performance of a sequence of positions. With meditation yoga the emphasis is very much on the spiritual aspects of the practice.
Practitioners believe that Sahaja can awaken the Kundalini energy. This energy passes through 5 chakras to reach the 7th chakra (Sahastrar).
Here it encounters 1000 nerve endings of the central nervous system, which are enlightened and nourished by the energy.
This can produce a higher state of human awareness - you will feel stress free, part of a collective consciousness that believers hope can work silently within us to transform the world.
If you are looking for a more spiritual approach, with the emphasis on the more cerebral aspects of the practice, then this may be the technique for you.