What is the best lens for this situation?

Did you say if you had to crop the image?  Cropping magnifies motion blur and noise among other things.  Since they are moving it would help to get the shutter speed up so that might mean a faster lens.  One way is to set the exposure bias a stop or two down and then pull it back in post.  You might be doing that already since the orig looks pretty under exposed.  Modern cams usually have enough DR to do this.  I'm thinking a faster lens, like a 77mm f/1.8 fer instance.