... bigger and faster is always better.
It's really a budget issue more than anything. People generally buy cheaper because they don't have the money, and it gets the job done. No Macbook user in their right would turn down a MacBook Pro, UNLESS size is an issue., Macbooks are nice and small. If you do have the $$ for the MacBook Pro, you will very happy, especially if you will running Aperture or Lightroom and Photoshop etc.
If you aren't totally set on OS X, the Dell XPS line is smoking!, and they actually have really good service.