This discussion is for people who have watched dbz as whole.

i think it will be majin boo the thin one then cell, he had hard time fighting this two. in cell saga he pass it to his son gohan the battle in which he said that gohan is now the strongest person in universe. thin boo is hard to fight as well because he suck gohan and the two kids who fuse but then being in super seiyan level 4 gokou surely is the best. ^.^ he looks so cool in super seiyan four.

Majin buu offcourse bcoz goku had to take it to next level and tranform to supersayan three...And buddy you should watch dbz gt man its awesome no fillers quick action...

well if you ask me the toughest opponent was cell cuaz goku was unable to defeat him and only gohan was able to defeat cell cauz he was able to surpass ssj and they have not mentioned in the episode but he transformed to ssj2 during the final kamehameha attack with cell if you have not noticed then you have to watch it again!!!! How can you include majin vegeta he was only controlled by babidi only for time bieng and only because he wanted to become stronger than goku!!!! The second best tough was majin buu and goku also enjoys the fight and wishes majin buu to return in human form so that he can train him and that's where uub comes!!!

since you mentioned DBZ as a whole, then i'd pick Broly. having eternal grudge to Goku his entire life was one hell of a reason to pick Broly as the toughest. my fav attack would be Cho Genki Dama.

Why you didn't include Raditz and Vegeta (only majin)? for me: Frieza, both physically and psychically. Frieza was definitely the most cruelest opponent. Goku really gave his all to stop Frieza. After genki dama he thought it was all over but the nightmare continued. He watched his best friend die in front of him. In the end, he turned into super Saiyajin because he couldn't take it anymore. I can't see Cell as his toughest opponent because he totally underestimated him. Goku knew from the start they will defeat him and he even let Gohan fight him. I don't even remember Goku fighting against androids (but Vegeta had hard time with #18 heh). I hate Buu. It was totally forced. Only thing I like about Buu saga is Goku vs. majin Vegeta fight. But even with Vegeta gone crazy I see it more as a friendly fight. Kamehame-ha is my favorite attack. btw who do you think was his toughest opponent?

I would say cell but I think majin buu was. I mean yea freeza was the cruelest of them all but buu could even kill freeza no problem.