I am still using the legacy animation, unless it's an humanoid character. For me (a programmer), it's easier to manage animations in the old system. I can freely add/remove animations, set its timing/layers etc. It doesn't need another file to get a GameObject animated. The Mecanim is good for artists and programmers working independently. And it's easier to create smooth and complex transition. But for a small develop team, I don't think we always have enough content to enjoy its benefit rather than pain.