my jee main rank is 21400 which colledges best for me

Hello, your rank is good to get a good college.
As you have not mentioned your category so I am assuming you to be in general category and at this rank you have good chances of getting CS,/It /EC in many IIIT, North Eastern Nit, also branches like biotechnology ,production engineering, mining engineering  are good options in some top Nit.

Also apply for Jac Delhi counseling.
Apply for Jossa counseling and then for Csab counseling.
If you wait till special round of counseling you would get a good college.

Refer to this link it will help you

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

All the best.
Hope this will help you.