Naik is a bit bombastic and actually appears desperate. He keeps citing verses with chapters numbers from the Quran or Gita to show how learned he is. It may look like smartness to some, but in the context of religion, it looks more like insecurity. Naik may be a good speaker according to some but he clings on to the books to sell himself. Thus, he lacks the real insight on the working of the human mind and how it absorbs all this information. That style might appeal to some wannabe academicians (who don't know the Quran very well), but most people would find it all rather boring.
Sadhguru is not only knowledgeable, he has the panache and puts across his knowledge in a style that would appeal to a large section of the masses, most of whom, lets' admit, don't really have much religious knowledge. You will never find him citing verses and chapters from the Gita or anything other book. He is much more effective in swaying audiences.
Both are well read, but IMHO, Sadhguru will wipe the floor with Naik in a debate.