Well both Delhi and Kota are good places to do JEE preparation. Both places have many good coaching institutes. However what matters is the fact that u do hard work .. okay ..
Well the study material of Brilliant is better however the classroom coaching of Vidyamandir is better ..
Again such things are perceptions that a individual has .. all depends as to what u like ... Also I will suggest that once u join the coaching institute then study material that those suggest you to do so that there is a better coordination between you and your classes ...