I was recently in Goa and again going to Goa this month end.
Of all the beaches that I have visited in South Goa, it is definitely Arambol Beach.
When 10 of us went there around 5 PM, we could hardly find any people there. The beach is very beautiful and the rocks on the beaches add beauty to it.
We spent the ENTIRE night at that beach and left from there the next day early morning.