What type of computer is best for animation work

None, you are better off with a desktop, with a laptop you are stuck with the video card and just about any other component that comes with it. Desktop you can upgrade and get faster components without needed to replace the whole thing.

But if you really want to get a laptop, Lenovo ThinkPad W series is good.

Basically, in a laptop, you better buy top of the line now as you can't upgrade it easily if at all.

Dell Precisions, HP Pavilion DV7 series, Toshiba Tecra R850 series with i7 CPUs, things like that.