Which one is best for jee mains online or offline?Kindly give a gd advice.

Giving the online or the offline exam completely depends upon you if you are comfortable in sitting in front of the computer for about 3-4 hours continuously then you should opt for online exam otherwise you should give the offline exam if you are comfortable with pen and paper
Also there are some advantages of online exam if you wish to give the online exam then you would get one week extra for the preparation of this exam apart from this there is a option for every question that you can change its answer later if you have any doubt this is the best advantage of online exam.
You can mark your doubtful questions so that you can attempt them in the end. this feature is called flagging
In an online exam.

Both have some advantages or disadvantages,but according to me offline is better because in last few years online paper is much harder than offline paper.