imo.. the vxl is a great set up for the begginer and for the money. but lets be honest the vxl esc is just plan junk. the solder joints come apart on most and there is no adjustablity at all. but on the other hand i can't say enough good things about the motor. it stay nice and cool, has plenty of power and torque and can get a hell of a top speed.
the mamba on the other hand also has its ups and downs. the esc is great. the programming is awesome and can handle more power then the vxl. but on the other hand the motors do run alot hotter then the vxl.
my suggestion would be buy the mamba max esc and then get the vxl motor. this way you get the best of both worlds. it'll cost you little more this way than just buying the vxl set up but still cost a little less than buying the mamba set up. vxl system-$160 mamba system-$220 buying them seperate to make a complete system right around $180-$200.
and always remember you get what you pay for