Honestly, it's pretty much anyone other than who they really took lol
In 2014, you could really justify taking Gordon, Exum, Smart, or Randle at the #3 spot and be better off, though I don't like the fit of Randle with Noel since neither can really spread the floor at all.
In 2015, obviously Porzingis would've been a hell of a fit next to Noel at the 4, though I think long-term he's still a 5 rather than a 4. Any of those other guys would've been better fits, too, though some of them would've been a stretch at the third overall pick.
If it was me, I'd take Smart in 2014 and Porzingis in 2015. Gordon would be a close second in 2014, but we've seen how bad they can be with a gluttony of frontline players but no real backcourt. Going into the 2016 season with Noel, Smart, and Porzingis, I don't think they'd be nearly as bad as they were this year.