Answer : You want to pick something that matches and reflects the style of your home.
In any room, color is introduced with paint, wallpaper, clothing etc. So picking a couch color is no different than choosing paint or wallpaper for the walls of your living room. Your design choices should reflect what you're trying to create for yourself in this space – an inviting place to lounge and entertain guests perhaps?
Get started by looking at what colors dominate in the space - are they sleek and modern or warm and rustic? What furniture items are currently in the old through judicious placement of new pieces.