I'm a little more willing to gamble on Griffin because the C's are playing with house money right now. They weren't supposed to be this far along in the rebuild at this point and they have some young talent (Brown, Fultz, Brkln '18) that will barely be entering their prime when a Griffin contract expires in 4 years.
And even if Griffin busts, I think the cap stabilizing will make big, expiring contracts valuable like they were before the cap spiked, which means if the worst happens, the contract might only be onerous for 3 years, during which the youngsters are developed. But if it does work, we're contending right now.
All of that is to say that I'm more willing to take a gamble than I otherwise might be. Griffin is the much better fit, Hayward is the safer bet. But Griffin also has the higher upside, IMO. I think I'd go Griffin.