At gunpoint I'd probably go with Rooney in the post-Cristiano era because I think he helped his teammates a lot more and just played as a 10 because Chicharito, Berbatov and Van Persie were all better than our #10 options.
But it's close, obviously. Looking at the current squad for example, you'd go with this I think:
Rashford----Rooney-----------
-------------------Bruno---------Antony
as a front 4, but if Rashford was out, you wouldn't pick Rooney, you'd probably take Van Persie because our wingers don't really cross it and like to link up more:
----------------Van Persie-----------
Sancho------Bruno---------Antony
looking at the other top 7 and their teams, I think the following would be their answers if they had to/could replace their best #9 with any of those 3:
Arsenal - Van Persie
City - Rooney
Liverpool - Rooney
Tottenham - Ruud
Newcastle - Ruud
Chelsea - Ruud
so basically if your team/attack functions well, you probably want Rooney's all around game or Van Persie's technical skill and ability outside the box, but Ruud is the safest option and if I wasn't sure what my best attack was I'd take him.
But if you look at the best teams in Europe outside the Prem, I think Bayern would take Ruud, Madrid and Barca would take Van Persie, PSG would take Rooney (need workrate to go with Messi and Neymar/Mbappe) and Napoli would take Ruud.
All-time United Prem team, if you figure it's:
-----------------Striker--Ronaldo---------
Giggs-------Scholes-------Keane-------Beckham
I don't think you'd pick Ruud over Rooney or Van Persie.
TLDR: Van Nistelrooy guaranteed goals, but Van Persie for us and his last few years at Arsenal did too with better link up, Rooney at peak best overall player. So it's like a 40/40/30 breakdown for teams based on their wingers and if they play direct or not.