I spent 4 nights in Arambol (Harmal) beach, which is the northernmost main beach in Goa, keeping in mind that Goa is about 100km long from north to south, as the crow flies. Plus, if you want to leave by long-distance train or plane, you have to back to/near Margao/Madgaon anyways (originally I wanted to go to northern beaches because I though it would be a little more “on my way” to Mumbai, but no).