I may get 45-50 in GATE 2017. I may not get Iits or Nits. is it better to join State level best colleges or go try next year??

If you are getting chance to get admission in good Govt state college then you can go for it or else if you think that you can crack the Gate 2018 surely then you can go for job along with that keep your preparation ON for Gate 2018. And one more thing which you can do is this year BSNL is offering 2510 vacancies JTO in the discipline of Telecom, Electronics, Electrical, Computer Science, Instrumentation and Information Tecnology on the basis of valid Gate 2017 scores so you can try there also if you belong to above mentioned branches.

For more information about BSNL recruitement, you can go through the below article as well-
http://www.engineering.careers360.com/news/bsnl-announces-recruitment-of-jto-through-gate-2017-214850

So decide wisely.

Good Luck.