which is better option after bsc phy hons 3 rd year ,CSIR NET or GATE..????

CSIR NET and GATE, both are some of the major exams in India. Both exams aim at determining the ability of any student in any specific Science Streams.
GATE is all India Entrance Examination conducted by IIT's and IISC. It's scorecard can be used for admission in various
Doctoral Programs and Master's program.
CSIR NET is conducted to look for science background talents for Lectureship and Junior Research Fellowship. This exam is conducted for Physical Sciences, Chemical Sciences, Mathematical Sciences, Earth Sciences, Life Sciences and their related subjects. Those who completed their Graduation and post graduation from science stream are actually eligible to appear for this examination.
It solely depends on you, how you want to see your future, GATE qualifiers career are inclined towards engineering field, they can also get job in PSU, while CSIR leads your career towards research, Lectureship and similar opportunities.

Know more here:
https://engineering.careers360.com/articles/gate
https://competition.careers360.com/articles/csir-ugc-net
Good luck!!!