Join the firm which is concenient to you as per location, timing and it adjusts your studies schedule. Learning is process. It never ends. If you think you want to learn all things in 42 months it is not possible. Choose what suits you and there they accept you. Not to worry.
Ask your Seniors and Super Seniors about the environment. In case you are not able to get then ICAI Office has advertisements of the vacancies.
Good Luck.
While selecting an audit firm u may consider certain aspects like....type of exposure u desire, leaves, coaching for ur PCC and final course, stipend amount etc.... i can suggest u some firms if i know in which place u want to do ur articleship..........all d best