I think it really depends on the individual. In my opinion I think a great jiu-jitsu game makes a solid mma fighter. Others think its the stand up game that is more important. But definitely get good at atleast one ground or standup art before you venture into mma.
People may disagree on what im about to say but I stand by my belief. Anyone can knock anyone out but when you're on the ground with an expert its a whole different world.
Others think a stand up game with enough ground skills to survive is the way to go... its all about your personal strengths.