It depends to which state you belong, as in different states the coaching institutes level differ. However , you can try for these institutes : Vajiram and Ravi IAS coaching centre  Delhi , Plutus  IAS coaching center Delhi , Shankar IAS Academy in Chennai ,

These are some top institutes , as you had not mentioned the state I suggest you to opt for the coaching institute which has a good track record , nearby your resident , good study material , has good faculties and have a good Mock test facility.