Although the atmosphere at Sisters' is great for homework and the many couches make it very comfortable to sit I have only had one employee there make me feel like I was their friend and very welcome there. They do bring you your coffee rather than calling it out but it seems more like they do it out of duty and not for actual service. Great coffee but lacking in a friendly, personal touch.
Bucers is by far the best option in Moscow for coffee. I've been to just about every other coffee shop in town and none of them compare. Everyone who works there, including the owner, make you feel extremely welcome and their coffee is self roasted on-site. I'm very familiar with the coffee world and I have yet to try a roast of espresso that beats Bucers. Go there, you won't regret it!
Fine coffee and beers on tap, warm and friendly atmosphere and great service. Best gathering place in Moscow.