Let's Make Robots!

Motor controller

Hello everybody,

I cannot figure out this by myself, on a first quick look over internet. 

I have two motors RS550s like this (http://banebots.com/p/M2-RS550-120) and I want to buy a proper controller for them. I had a look on these two: http://www.robotshop.com/eu/productinfo.aspx?pc=RB-Dim-30&lang=en-US or http://www.robotshop.com/eu/productinfo.aspx?pc=RB-Dim-42&lang=en-US but, I don't know which one is more suitable for my project. 

What do you think ?