Niyama - the second limb of Yoga

Niyama is the second  (out of eight) limb of Yoga.
Practicing the Niyamas helps to channel the energies of  the sense of perception in the right direction.
It contains five personal practices:

1. Saucat - cleanliness, purity
Purity and cleanliness protect and purify the body and make it a fit home for the soul
The Yoga Sutras of Patanjali, 2.40, Iyengar's translation.
2. Santosat - contentment 
From containment and benevolence of consciousness comes supreme happiness
The Yoga Sutras of Patanjali, 2.42, Iyengar's translation
3. Tapas - self discipline
Self - discipline burns away impurities and kindles the sparks of divinity
The Yoga Sutras of Patanjali, 2.43, Iyengar's translation
4. Svadyaya - self study or reading the scriptures 
Self study  has two paths: One is for communicating from skin towards the soul. The other from soul to God The Yoga Sutras of Patanjali, 2.44, Iyengar's translation
5. Isvara Pranidhanat -  surrender to the Divine.
Serender to God brings perfection in samadhi (the final stage of the practice) 
The Yoga Sutras of Patanjali, 2.45, Iyengar's translation

Which Niyama is the most challenging for you?