Depends on person to person. While some candidates prefer the conventional method of pen and paper, some are comfortable with the online mode to. The one advantage is that Online exam is conducted a week after the offline mode and so you get an extra week to prepare. Also in the online mode you can go back and change the answer you marked before final submission but in offline mode once you have marked an answer you cannot erase the ink. 

But again, I'd like to reiterate that it solely depends on which mode you think you will be comfortable in and opt for it accordingly.