a mbc is limited to just raising and lowering boost pressure. There is nothing to be good about turning a knob left and right.

a 3 port has the ability to perform;

1. error correction (closed loop control in positive boost pressure) 2d
2. ability to increase wgdc during an active boost curve in 3d mapping
3. ability to decrease wgdc during an active boost curve in 3d mapping
4. ability to set different boost levels based on what gear the transmissions in 3d mapping

1. is nice because you can have it correct or under correct the tune by itself based on error correction table. You can also disable this feature.

2. is nice because you can further control torque easier, same with 3. Or you can extract more power, by forcing boost pressure to hold longer at higher RPM on cars that are able to safely run the additional boost at higher RPM and granted the WGA allows for it as well (proper preload / spring tension).

4. is nice, because a lot of cars get loaded up more in 4th then 3rd on stock final drive, so you can lower the boost in 4th only to eliminate detonation, while not having to limit 3rd gear by lowering a mbc which globally affects all gears, where as a 3 port can adjust one particular gear only.

Additional: While at the drag strip, if theres a very high HP car blowing off tires in 1st and 2nd, and he needs to limit his power to gain control of his car via traction, he can lower boost in just 1st and 2nd only, then have it kick in full in 3rd-4th+.

There is no debate, a 3 port is superior to a mbc in every way, shape, and form.

That said, I prefer them both together on certain setups and that type of technology is nicknamed hybrid boost.