If you can only do one and you are more focused on MMA than BJJ, do the nogi as it will be more practical for MMA. Not that gi isn't effective, but you will learn a lot of techniques that require the gi that won't carry over into MMA.
The 2014 Hit Squad (FFL)
Eddie Alvarez - Junior Dos Santos - Patricio Freire - Jessica Eye - Pat Curran
Sig Credit: M.C