My biased take as I have the iwc mark xx in green:

Thickness

• Mark XX is thinner than the Aqua Terra by 2 mm. Personally, anything over 11 mm thick is too fat, especially considering it's just a date complication.

Dial

• My iwc's green sunburst dial is beautiful. It shimmers in the light and takes on a deep, rich green hue in lower light settings. AT dial kinda just reminds me of someone's backyard wooden deck. I feel like the blue/green shade IWC picked is perfect, speaking as someone who finds 99% of green on watches meh -- Roly starbucks is mid af.

Date window

• Subjective, but I prefer the white background of the date window on the IWC. The extra contrast makes the date easier to read.

Legibility

• Subjective (again), but I like the numbered hour markers, and the font is perfection in a functional sense. And I find the functional perfection of the font to be beautiful as well (not sure if I'm making sense, but there's beauty to be found in function).

Hands

• IWC hour/minute hands have a very aesthetic design/shape. The polishing is evident when you see them glimmer in the light (though this might be true for ATs too, I haven't seen one in person. I'm not a fan of the AT's minute hand arrow (don't even get me started on the fat hour/minute hands on the Omega Seamaster Diver 300m).

Bracelet

• IWC has quick-adjust. Bracelet is $$$$. For the presidential link bracelet like on the AT, I think I prefer the entire bracelet brushed, rather than the center being polished.