Dan, they are both great hikes, but with caveats.
Sutton Peak is shorter, more remote and more exposed. The last stretch is not really much of a trail but a bit of light bushwacking to the summit. And the summit is like a real summit.
Santiago is a longer hike with more diverse terrain. It’s much higher, with much more vertical gain (4000′). The summit is rather anti-climactic, because it’s not a sharp, distinct peak and it has a cluster of radio antennae. But the real show-stopper for some is the road TO the trailhead. It’s a dirt road that definitely requires a high clearance vehicle.
Hope this helps!