the first game of my browser games list is obviously AQW I also play Drakensang when i hav free time (almost never)
Usually when I find a free game to play, I stick to that game. I would say AQ3D since I've accumulated 5,183 hours.
Nowadays, with adult-life I stick to AQ3D as my #1 free game. Also because AQ3D doesn't drain my wallet with virtual currency like a few years ago when I played multiple free-games at once. I try to stick to one for now and switch off between console and AQ3D.