My money is on destiny soley because of how many things he'd have to deal with and he doesn't have the mentality to try to wipe out a universe. He always wants a fair fight til someone admits defeat where as everyone else is aiming to kill. Not to mention how technical some of the bosses are and what has to be done to beat them. Id bet more on lord bills, whis and even majin buu (kid) over goku. If it was gokus power mixed with bardock and vegetas mindset I'd say goku but that's the only reason.
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He loses those thoughts at super saiyan three and fights on instinct and wouldnt let you anyone kill him so its even harder for guardians to defeat him
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He said universe not just guardians. I doubt he'd be able to figure out the vault of glass by himself. Yeah atheon can teleport him and he can use instant transmission to get himself back, but unless he takes the relic with him, which I doubt he would, he's done.
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He could instant transmission to the relic and get it
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He doesn't know what it is. He has no one to assist him. Plus its a different time, so he's stuck and going blind in the past. Whether he destroys the oracles (doesn't know what those are either) or not he still can't make it back.