Both were designed by Dave Johnson. In performance they are more similar than different. So ask yourself if you want a meter id system. If so, get the MXT. Do you want to be able to hip or chest mount the control box? If so, get the Lobo. Would you like a dual tone id system (low tone bad, high tone good)? If so, get the MXT.
For just straight up nugget hunting I tend to lean towards the Lobo. For multi-use, like coin and jewelry and relics, etc. I'd tend to lean MXT.