This was our second time staying at Susan and Amit's flat. Having gone to university in Edinburgh and knowing the city inside and out, I can tell you this flat is PERFECTLY located in grassmarket. You can get to tollcross, Newington, new town, and anywhere else you want to be. A run of historic pubs are literally across the street from the flat. You can see the castle from your front porch and it's a 10 minute walk to get there or the meadows. 5 minutes gets you to Cowgate or the royal mile.
Susan and Amit are extremely responsive and checked in with us regularly. The flat was immaculate, as it was the last time we stayed. They have an iron and ironing board, a number of hairdryers (which my wife ook advantage of), and a kitchen with all the utensils you could need. And the pice for a night there is unbeatable for the location. I would live there if I could.