Well it all depends on various things such as contract and role.
If we just told him come here and you have to fight for your place - The best thing for him is to sign for Dortmund and Raiola isnt stupid. You can bet Raiola would have pushed him to Dortmund regardless as he is way more likely to command a high transfer fee from Dortmund than from Juventus.
At Dortmund he has a known attacking style which favors their CF - Perfect for someone like Haaland
At Juve you have a team in identity search - We want to be an attacking team but still cant find the balance doing it. If you go to the Allegri days its even worse as the style is not attacking enough for him to shine the way Raiola intends.
So its not just black and white

, its more of a question of various things in which will provide him the best way to develop.
Im not a football player but as a kid I really liked Zola and even cheered for Chelsea (after Juve ofcourse).
Should I be given a choice - Chelsea or some other club - I`d pick the one that suits me the best and not just because the team has a player I really like.
Players have brains and when they dont have it their agent uses his for them.
The best move for him was Dortmund. I know it Raiola knows it Haaland knows it, most of the forum know it and I think deep inside of you - you know it too.