I have to say: Goro all the way!!!
Goro is a legendary figure whose status in the MK canon is much more important than Cyrax's (no offense to him; he's cool too).
It's interesting that you note that Cyrax has been both a hero and a villain, because the same thing has actually happened with Goro; right around the same time as Cyrax, even! There was a point in time (in the original timeline, before the reboot) where Goro redeemed himself and changed his ways (for a while), becoming best friends with Kitana and helping her lead the charge against the last remnants of Shao Kahn's empire before the Deadly Alliance took over. It all started with Kung Lao's ending in Mortal Kombat Gold (which was canon at the time), which shows a rare example of Goro's noble side.
https://www.youtube.com/watch?v=e0WPC7Z5oEIAside from that, I feel like Goro would be a much more unique addition to MUA. Again, as cool as Cyrax is, MUA already has plenty of robot/cyborg-type characters on it's own, both playable and not, while there's nothing quite like Goro in there.
Plus, who can forget the feeling they had the first time they were playing the first Mortal Kombat and saw that four-armed monster?!? He was so fittingly terrifying and awesome!!! Getting to bring that fearsome might to the Masters of Evil would be such a powerful feeling! He's called the "Prince of Pain" for good reason, after all! I always felt, personally, that Goro had some of the most painful fatalities, especially in the last two Mortal Kombat games.
As for his moveset, I think it could provide an interesting enough variety. He's been able to shoot fireballs, breathe fire, do spinning attacks, jump with such force it shakes the ground, have a boost that makes his physical attacks cause fire damage, wield four bladed weapons on each arm (similar to a Tarkatan's blades even), have all kinds of great grab/grappler attacks, roar intimidatingly; all pretty cool things, I think. Plus, in some of the games like MK4 and MKX, he's been shown to be alarmingly and deceptively fast, which makes him even scarier and more powerful, I think.