If you want to Kick Butt on Robotron, forget either of those sticks, and try to get hold of the real Wico 8way leaf sticks. There simply is nothing that beats them for that game.
I love comps for fighters, but gave up when trying to use them when playing Robotron.
As for Rotaries, the Mechanical are best for certain Rotary games because they lock in the correct angles. However, the feel of the handle probably wouldnt be the most conductive for typical long play.(has octagon shape with hard angles)
The optical rotaries that happs made, are built like Supers, and might be ok if you like supers.(and dont mind the difference in gameplay on the mechanical rotary games) Personally, I cant stand them. Supers are horrible for fighters, where hitting perfect diagonals, is critical. They also are a bit mushy and fictionally-resistive feeling. Not as smooth, light, and quick as a Comp.
Many 4 way games can play 'OK' with an 8way. But the difference with a true 4way restricted joystick, on a game like Ms Pacman, will be night and day. No getting stuck or the game thinking you meant to go a different direction. Faster and easier movements, because of the diagonal guidance of the restrictor edge.
You can cut a cabinet side with a jigsaw... but with a circular saw, it will take a 10th the time, and provide a better cut, and better user experience (less hand fatigue & aggravations) Theres a reason for the differences in the tools, and thus the differences in performances...
Sometimes theres really no way to get around things. If you want better control and an overall better experience, you have to have the right tool / controller.