I have Scored 81.65 percentile in cat , having experience in marketing for 18 months. Please suggest me the best college .

Hello arun,
Well arun you got a decent score of 81 percentile and its good that you have 18 months of experience. You have a good chances of getting calls from good b-schools like alliance school of business, nit rourkela,
Delhi school of management, Delhi. Birla institute of technology, mesra and various others are there that suits your profile.
I am giving you one link and it will help you finding colleges of your choice.

https://www.google.co.in/amp/s/bschool.careers360.com/articles/what-if-my-cat-percentile-between-80-and-90-do-i-have-any-chance-at-top-b-schools%3famp

I wish you all the best.

Cheers !!