Depends on what type of animation and what style of graphics. 1. Photoshop is good. 2. If you want to do IK(Inverse Kinematics) or bone based animation, then there are some good tools out there for that such as Spriter, and another is Spine by Esoteric Software. 3. Hexels is also an awesome pixel/trixel tool with animation built in (this is what I've been mainly using at the moment) great for doing pixel graphics as well as isometric designs
