For me, the choice was easy because I never use the numpad on any fullsize I ever type on. I can understand it'd be a little more difficult decision for those who use it from time to time. My reasoning was, as others have stated, you can always get a standalone numpad if in the future you decide you need it, and have greater flexibility that way.
But again, it's a personal preference thing. Examine how you operate, what you are or can grow to become most comfortable with and what direction you want to go in, and then try it out.