I think Uro, Titan of Nature's Wrath will see a lot more play. Both in and out of the Command Zone. Gaining resources is always rated more highly than pissing everyone else off.
I think I'll see him more out of the Command zone, but I think there's a lot of capability to build around him as well.
On first cast Uro, Titan of Nature's Wrath is essentially a Growth Spiral in the Command zone - that's pretty cool as is, especially since you're not likely to need to ever pay command tax on him afterwards either, unless you want to. You could even let him return to the CZ on the first cast, just to allow yourself the latitude to play him for 5 as ramp if needed, though I doubt that would come up often.
What gets crazy is when you add value to him - You're casting a creature, there's an ETB trigger, there's a card draw, there's life gain, there's potentially a land etb, and there's a death. That's a LOT of things to work with:
I don't think I need to list every landfall ability, but you can get a lot of tokens.
I mean, I'm already imagining someone dropping Uro on t3 for a growth spiral, letting him go to CZ, in order to play a Greater Good and then be able to draw 7 for 5 mana, discard 3, and be well on the way to recasting him from the GY.
Now, I think that's a bit far-fetched. You're probably better off leaving him in the GY after the first cast, and using blue filtration/loot to stock up the GY to recast him. Frantic Search could make an appearance in that deck, as could Windfall, Tolarian Winds, Flux, etc.
He's rather open-ended to build around, and even if you DON'T - many of those cards are just good in other decks, and can easily be run alongside him. I wouldn't mind him in the 99 and drawing him early, or even drawing him later. Especially not if I have a greater good.
Kroxa, Titan of Death's Hunger I don't see being included as much in the 99, but he could make an interesting type of Megrim commander. You can probably power him out earlier than Uyo thanks to cards like red wheel variants - red has plenty of looting as well, while black has plenty of draw, and plenty of discard. New Chainer could fit the theme well.
T2 Croxa, T3 Wheel, T4 Croxa is probably a dream, but a scary one nonetheless.
I love these Titans for my commanders all I need is Infinite colored mana and poof you win the game. Im looking for some synergy cards though, cards with effects like Equilibrium but instead of cast trigger to return creatures, I need ETB triggers so I can bounce these titan back before resolving the ETB trigger.