My company is willing to reffactor its biggest and heaviest project introducing some kind of framework. Are there good online source/issue/blogpost with comparison of these 3 frameworks - Robotlegs, Swiz and Mate?
I don't think a comparison is the way to go. They all have strength and weaknesses. It all comes down to what you're trying to accomplish.
With that said, my 2 personal choices are RobotLegs and Parsley. RobotLegs is good for small to medium size application since it's easy to learn and use. Parsley is more robust and adds a lot more features than RobotLegs, which is why its been used in the world's largest flex applications. From your description, it seems this is a large project, then I would recommend Parsley, but maybe you don't need all of it's features.
Best thing you can do is try both and see which one fits best.