Wow! Two really close players here. Let’s take a look. I have Russell Westbrook as a top 10 PG and James Harden as a top 10 SG all time.
Scoring: Harden. Westbrook is a great scorer but Harden scores really effortlessly, he’s also better both at FTs and from 3PT range.
Assists: tied. When Harden plays the PG position in the D’Antoni system he can average 10–12 assists a game. Westbrook can average a triple double so he can also average over 10 assists a game.
Shooting: Harden. His TS% is higher, and as I mentioned is a better FT and 3PT shooter than Westbrook.
Defense: tied. neither are great defenders, none have ever been all-defensive and both average around 2 steals a game.
Awards: tied. 1 MVP and multiple All-NBA teams for both. Neither have any rings.
I would take Harden slightly over Westbrook just because of his ability to exploit the game for points using free throws. Westbrook will get you that triple double but he mostly makes the rest of your team worse while doing so. Harden seems to elevate his teammates more than Westbrook does.