I’ve never been to Iceland.
I have used both. You’re very fortunate to have this choice.
There’s a considerable weight — and price — difference between the two. I think you could buy two X-Mids for the price of a single Aeon Li.
If your goal is to enjoy the scenery while in camp, the Aeon Li opens up more fully on one side than the X-Mid but the X-Mid opens on two sides (please somebody correct me if I’m wrong about the X-Mid’s inability to open fully on one side. I vaguely remember that you need one of the two side panels deployed to get a taut pitch, but somebody with more experience better confirm that before it becomes a thing). I prefer the former by a long margin. YMMV. If you carry two poles, the Aeon Li would allow you to use one pole to pitch camp and another pole to use while sauntering around camp. The X-Mid will be more comfortable if you’re spending hours and hours inside due to the extra internal volume, but the Aeon Li is hardly cramped.
Pitched properly (really quite easy for both), both are very stout in storms and moderate winds. The X-Mid gives you slightly more protection because it goes down to the ground on all sides. If the Aeon Li is positioned right (with any of three sides but the front pitched into the wind), it will deflect much less in strong wind than the X-Mid. The triangle formed between the two struts and the center pole on the Aeon Li is very strong, as in zero deflection. In my experience the X-Mid will deflect a lot in strong winds, but it’s not really a problem. Whichever one you pick, bring a few really good stakes.
I’d bet that the X-Mid materials will last longer, if long term economy is a concern. Plus the X-Mid is a priced at a level that shows appreciation for mere mortals. Silpoly is reputedly more environmentally friendly to produce than DCF. I haven’t read anything about the environmental impact of disposal for either material.
Both look equally nice in photographs. :-)
Can’t go wrong with either.
Personally, I’d choose the Aeon Li, just for the weight savings if anything. I’m also partial to monopole designs. (For those looking to buy, I’d also suggest a silpoly Pioulou from Tipik, but the lead times are very long now).