Juventus becomes the best club for him next season. Lukaku have two best options for now.
1 Juventus
2 Saudi clubs
I don't see a better choice than those. I hope lukaku will able to decide it as soon as possible.
Lukaku have rejected with all interested from Saudi Clubs and seems he won't play there any more right now although has chance for few years later depend on how excited salary accepted. Last option for Lukaku between returning back to Chelsea or join with Juventus next season but need waiting done deal transfer fees with Chelsea. Its not easy for getting done deal about transfer fees after Inter Milan withdrew for signing Lukaku after second proposal with 35 million euro rejected by Chelsea.
Juventus is bigger teams and Lukaku have been adapted well with Serie A competition, its not difficult for adapting again for Lukaku if join with Inter Milan rival teams next season because regular position is most important for Lukaku than returning back to Chelsea where difficult to be main player under Pochettino.
It is true that he did that for now but as the transfer window comes closer to the end I think that Lukaku could also reconsider his rejection and go for it if Chelsea doesn't agree to the deal with Inter Milan. But his position isn't hopeless as Chelsea would like to get rid of him as well to have more financial scope available for new players. Lukaku would mean another player on the salary list without actually being one of the desired candidates for Pochettino. They will try to avoid that situation and in the end let him go.