I'd start with reading our reviews. They are much more detailed than any answer you would get here.
So go to http://www.cnet.com/topics/phones/ and start reading.
Suggest me good smart phone within 30,000/- INR (500USD)
Currently I m using nexus 5.
I was thinking from nexus 5x/6p or one plus 2?
Which one is better among those? And any other phone better than these?