Bansal Classes was the best coaching before 2010 as it had highly experienced faculty and good teaching methodology. At that time there was only one good coaching for IIT in Kota and that was Bansal Classes. It gave rank 1 five times in 2010, 2008, 2007, 2002, 2000. But after 2010, its faculties went to Vibrant, Allen etc and its downfall started. Right now Vibrant and Allen are much better. You can see their reviews in the following links.
https://ransphire.com/coaching/Resonance-Kota/reviews
https://ransphire.com/coaching/ALLEN-Kota/reviews
https://ransphire.com/coaching/Vibrant-Academy/reviews
https://ransphire.com/coaching/Bansal-Classes-Kota/reviews