This topic is common, but I'll add conditions that determine the eligibility of a contender you think could beat Goku, as well as circumstances surrounding the fight:
1: I'll elaborate upon request,I can't list it all, I don't wanna overlook something creating loopholes. Basically, no absolutes (infinite power), instant-type kills (Nigeki Kessatsu), invincibility/equivalent, specific weaknesses only(Shinigami/Death Note), time control, (Go kill Baby Goku), or most anything of these natures.
2: Specific Powers. I want a fight; no possession, mind control, ect. List someone suitable. Also, no Dragon Ball or non-canon characters (Jin Kariya/Bleach).
3: Tools. If they follow the same rules, okay.
4: 1-VS-1, no summons, tagteam, ect., but most fusions, multiple personalities, conjoined twins, ect., are okay.
5: Circumstance: Fight occurs with knowledge that it's to the death, in a neutral, empty, indestructable zone. Will elaborate upon request.
6: Detail your argument.