There are two things to look at with these systems. The first is their performance with native content like Atmos or DTS:X encoded disks. I think they seem very similar at this point but there are so few DTS:X encoded disks yet to look at. May not be able to directly compare them easily as Atmos disks play with Atmos decoding and DTS:X with DTS version so you can't compare the same source with the two standards easily.
Then there is the up converters that take a 2 or 5.1 channel source and mix them into the 7.2.4 or whatever channels you have and add height info from nowhere. This was a bit harder to compare at first as Denon/Marantz did not allow you to choose the up converter as it was based on the dolby/dts format it was in. But I think you could convert to 5.1 PCM in the player and then you could choose. And Yamaha let you choose in their just released firmware. So people have compared the two up converters on the same source and they found that DTS:X has a bit more dramatic height info with Atmos being more subdued. Which is better is really subjective though and will vary depending on content and the type of scene so I don't think anyone can really pick one as 'Better' than the other at this point. From a consumer point of view its probably best if we get to choose which one we want for each source based on our own preference. So hopefully they will unlock this at some point in the ones that are locked down right now.
Really the situation is about the same as it has always been with the previous Dolby and DTS competing standards from the past with Dolby_Digital/DTS, Prologic/Neo, TrueHD/Master_Audio and ProLogicIIz/NEO:X where they both come out with nearly identical standards and we can just pick the one we prefer for a given source but neither one is 'better' they are just slightly different.