Our software is Open Source. We choose to use Repetier Host for driving the printer and Slic3r and Cura for slicing, but you can use Pronterface (firmware) (or RepG ), or other Open Source tools as well.
One major reason we picked Repetier Host is that it comes with Slic3r and Cura completely integrated - so the use is pretty seamless - there's no fiddling with installations and integration. The other is that it has a built-in printer simulator, so you can take your 3D model right now, run it through the software, and see what the print would look like. It won't tell you whether the print is a practical one, but it will tell you what it will look like.