I voted for Hayes and Okwungu because I think they have the best long-term upside for the Suns.
With a core of Booker, Bridges and Ayton, the biggest impact in 2-3 years would be a starting point guard to pair with Booker or a power forward to pair with Ayton.
I don't think there is a player in this draft who will be either of those things right away. Toppin and Haliburton are the closest things to it; I think they would both make an impact right away. But in 3 years, if Hayes and Haliburton both work out, I think Hayes would pay off much more. In the meantime, he's still a nice option for a third or 4th guard while he develops.
Someone mentioned in one of these threads that you need a point guard to be able to create shots for himself, create shots for others, and defend. I think Hayes has the potential to do all of those things at a high level. Will he reach his potential? Who knows. But in this draft, that's good enough for me to have him as my top target.
I think Obi Toppin would come in and make an impact right away at a position of need. However, I'd rather bank on Okungwu's potential to extend his range than Toppin's potential to become a great rebounder and rim protector down the line.
You probably couldn't play Okungwu and Ayton together much to begin with, but if you can develop Okungwu into a fit with Ayton down the line...the potential is very exciting. In the meantime, he's an excellent option to back Ayton up and provide insurance for when Ayton gets in foul trouble.
In theory, Jalen Smith could be that fit right now. But if I'm being honest, he doesn't pass the eye test for me. I think he tops out as a solid role player.
I also REALLY like Devin Vassell. Having another guy like Mikal out there at the same time as Bridges would be a lot of fun to watch!