i would also go hyper 7 pro
as far as mugen bearing go i think they are pretty good i had a mbx4xr for over a year and never had to replace any bearings
the mtx3 bearings youve had problems with are the 10x15 bearings right? at least those are the ones i always had problems with thats why they switched front uprights so they could use the different size outer bearing because those others were constantly crapping out
i think that the main problem is either the size of the bearing or maybe the car is just extremely hard on them
the problem i have seen people with mbx5s having is the steering piece in the front where the tie-rods attach in the center called steering plate i think has been bendind mostly because those same peopl shimmed it up 3mm to reduce bump steer
i can see mine is slightly bent after 4 races first couple races i drove poorly and over shot most of my landings really abusing the buggy but didnt break 3rd race was at a track with a huge 6-7 ft tall table top and the 4th was the trinity gas challenge where i ran 60 minutes of mains and 4 qualifiers and mine is only slightly bent and nothing else is broken or worn or anything but ready to race
the fix is to get an extra plate and cut the ends off and bolt the 2 plates onto the steering arms together you then have spaced it up 3mm and enforced it so the problem is gone for $12 or so
i saw some broken arms at the race with the huge table top but nowhere else have i seen mbx5 break
as far as durability i think mugen may be the best and if not very close
i even ran my mst-1 for a 40 minute main without breaking