Sabo is by far the worst of the two. Ace (as a character) has/d plenty of shortcomings but still way better writing than Sabo has, others have pointed out the conveniently amnesia plot; it's retarded and makes it seem like a band aid over Ace's Death, Killed off one brother? Oh Hey here's another *whistles nervously*, Hey Let's give him Ace's DF wouldn't that be cool!
smh, God awful writing if I had to say. Cookie cutter material.
Sabo would have turned from this god awful written character (to me at least) into a good one through that process:
1- If Ace and Luffy's first mention of "Sabo" name was during their meeting in Alabasta, and NOT during Ace's death door in Marieford. That would have establised that he's NOT a replacement, rather someone truly existed and intended to be introduced later. And not at the last second LOL
2- IF, Oda would have given him a completely different DF ability. I would have loved a Zoan for him, specially since he serves "Dragon" a supposed animal name. And on top of it, he seemed to be a proficient close range fighter. What people do not realize is that Logia are NOT the best in close range combat. Usually it's Zoan as said by Rob Lucci. With Haki, Sabo would have created a completely unique fighting style that would have separated him from the "shadow" of Ace.
However, Sabo basically turned from "close range" fighter before his Logia, into a mid-range fighter, just like Ace. Which is bad because instead of making him more unique, Oda basically changed him from being unique into being a mirror for Ace.
And on top of that, he fucking had curly hair, how the fuck it became smooth? Couldn't Oda draw a badass brother who got afro hair? even if blonde? I swear, Foxy's arc with that afro hair got lots of attention for the afro hahaha. Oda could have made Sabo some real badass mofo with a big afro.
LOL, Sabo as a kid had every bit of a potential to be unique, but then come timeskip, and here Sabo makes a comeback, and suddenly, Oda is shifting him from being Sabo into Ace 2.0