Personally, I prefer Roman numerals for the Game Boy games, but since it's not universally recognized, I also specify the system.
As for my choice of Metal Man, well the Metal Blades are my all-time favourite Mega Man weapon for the original series. They're fast, can fly out in any direction, consume little weapon energy and you can have three blades on the screen at once. Nothing else has been that versatile in the Blue Bomber's arsenal since in my opinion.
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"With the first link, the chain is forged. The first speech censored, the first thought forbidden, the first freedom denied, chains us all irrevocably." [...] The first time any man's freedom is trodden on, we're all damaged. - Captain Jean-Luc Picard
B*tch, meet reality. Reality, meet b*tch. - Me