Should I choose GMAT/GRE? I feel I'm good at English BUT not sure of Quants.Is GRE also for management?What must be my first step to prepn?

I'm into my 3rd year of Mech Engg.I'm not sure of what to do in future.I like teaching though & I'm keen on starting my own school once I complete an MS/MBA.I wish to study abroad as peers say it fetches more reputation.Though many say GRE is easier,the QUANTS part haunts me.What should I do?MS/MBA?