MY PERSONAL OPINION & FRIEND'S EXPERIENCE !!!
It would be great if you opt for a mid-size firm instead of joining a Big 4. In mid-size firms, you would be exposed to all aspects of a CA practical training, i.e taxation (direct, indirect, international), auditing, company law, FEMA, etc.. This knowledge would help you in choosing your path after you pass out in Finals. Currently good stipend & nice work culture might lure you to join Big 4, but later you might relent on this decision. I know many of my friends (whom I met in GMCS) from Big 4 who are stuck within the same Dept. for years & are now left with very less option to move out (from Big 4) to find a new Career as their experience is restricted to a particular field.