Personally, choosing a road oriented (say, 80/20 road:gravel ratio) tire choice for the gravel bike was much easier. IMHO, the GP5000 700x32 is the clear choice currently.
I put the GP5k (TL) in 700x32 on my gravel bike for road use a couple months back, and have been really happy with them. I have a bit over 600 miles on them at this point, including a solo century ride. They provide a quite comfy ride for their volume, roll very nicely, grip when you want them to, and do fine on occasional stretches of hardpack gravel. I don't think you can go wrong with them for general road riding.
The Barlow Pass was a consideration as well, though there were enough forum posts about potential flat trouble with them that I decided to go with the GP 5k. Sure, flats happen, and maybe some riders push gear further than others. OTOH, too many flats get in the way of a fun ride, and there are plenty of goat's head thorns where i typically ride. If flat protection is a real priority, the Schwalbe Marathon Supreme looks like a good option and doesn't give up too much to the GP 5k in terms of rolling resistance. FWIW, no flats on the GP 5k yet.
I had some 35mm Ritchey Alpine JB tires on the gravel bike much of this year. 'Jack of all trades, master of none' sums up my feelings on these pretty well. They were a good choice most of the time when I had just one wheelset. After springing for a second set, it's easier to keep two types of tires installed and swap wheels instead of tires.
Last year, the Schwalbe G-One speed was my go-to tire for all-road purposes. They're great tires for those conditions and compare well to the GP 5k. They do wear a bit quickly though. IMHO, the edge goes the the GP 5k.
The Teravail Rampart is another interesting all-road tire. Picked up a pair of them in 700x42mm that I'll be putting on soon. I think they'll do better in the upcoming weather conditions than the GP 5k. Unfortunately I don't have any actual riding experience on them to share yet.
At least for me, choosing a gravel tire seemed to open up almost endless choices. My target for this tire was at least 50% gravel riding and something that rolls decently on hardpack (There's always some road riding for me to get to gravel).
Of the tires mentioned by the OP, I'd probably go with the Cannonball. It seems like the best balanced tire of the three, and I've seriously considered that tire before. Since the subject of larger diameter tires was raised, the Sparwood is a similar tire available in 2.1".
I can say that the Terreno Zero mentioned by
@smoothmoose is a solid tire. I've had those in 650x47 installed tubeless for a couple years, and really like them for rides that have a high degree of variability. With the smooth center, they roll nicely on hardpack, and the small knobs on the sides generally grip well when things get rockier. The one place I suppose they could be a bit better is transitioning into deeper sandy/loose conditions. In these conditions, they can slip a bit until they sink enough for the sides to grip the loose stuff, although this is somewhat expected given the tread. That said, I've never completely spun out in loose conditions, so I'm happy with them.
My gravel bike came with 700x37 WTB Riddler tires. These grip well and ride decently on gravel. However, they don't roll that well on the road, and I find a wider tire more preferable for gravel. Not a bad tire, they just kinda fell into a gap for the kind of conditions I typically encounter.
As far as other gravel tires I've considered go, Teravail just came out with the Washburn, and their Cannonball (or Sparwood if you have the clearance) also seems interesting. The Terreno Dry (XC if you have the clearance) should do better in loose conditions than the Zero. Having had a good experience with the G-One Speed, I'd consider the G-One Allround for gravel use as well. The Maxxis Rambler and Velocita, IRC Boken Plus, Donnelly Strada, Kenda Flintridge, Rene Herse Babyshoe Pass, and Ultradynamico Cava have also seemed potentially interesting to me.
HTH
