I had an Arduino Mega sitting on the shelf, so I started with that, then added the RAMPS 1.4.

I picked the RAMPS because I like the layout and the fact that I could pick the stepper drivers that I wanted, and it has enough I/O pins to add on all kinds of bells and whistles.

My only complaint, and this goes for many Arduino shields, is that the edge of the board sits right on the Mega's power and USB risers.
I ended up getting some stackable headers and raising the entire RAMPS by a half inch. In the long run, I think it will also help keep air circulating between the boarrds a little easier.