Hi,
I'm on H1B visa and my wife is on F1 visa (she has Graduate research assistanceship and her tax status is resident alien). We both are from India.

My question is:
Should we file jointly or separately to get the maximum return?

Thanks in advance.

Do your returns both ways and figure out.
Normally, it is always better to file joint return.
Read Your U.S. Tax Return: Filing Status for Married (http://taxipay.blogspot.com/2008/02/filing-status-for-married.html)

If you are both already treated as resident aliens, you will almost certainly owe less tax by filing jointly.