If one wanted to get into it now I might recommend starting from Steel Ball Run and seeing if they like it. SBR is in a whole separate continuity to the first 6 parts and while it does call back to them in slightly spoilery ways like the designs of some characters, there’s nothing that actual spoils the plot of the original continuity. It’s also a lot better written and drawn than the first few imo. Only problem is that Netflix are POS and releasing the episodes in the most convoluted way possible