Just the sword, all other signs point to Luffy.
Luffy is the man Oden and Roger was waiting for.
Yamato admitted Luffy was "more Oden than her"
Luffy is the man who found Momo.
Luffy is the man who allied with Momo.
Luffy is the man who gave Momo courage to lead and courage to put his life on the line.
Luffy is the man who fought Kaido 1vs1 already and is the one that will take Kaido down in the end- this is OP, do you really expect anything else?
There more than just that, Both Zoro and Oden are swordmen and connected to Wano
Both Are strong enough to have their own crew but decided to follow another captain
Zoro inherited his sword
There is more that i forgot but you get the point, Its not as clear to either way, But because of the Wano backstory i thought Oden and Zoro are parallels. But like i said it doesnt matter what i think its all what Oda thinks, Unless hes going to pull something like Both luffy and Zoro share the parallels with Oden, Its will be what Oda wants which is as of now Luffy and Oden are parallels