U12T is definitely more airy, more balanced, and more mature sounding. It’s closer to my ideal signature as well. Prior to MEST it was my favorite IEM, after eclipsing Campfire Solaris.
I really loved Andromeda, but it was too bass light for me. Solaris offered a similar sound signature, but with beefy DD bass. It was exactly what I wanted. But then U12T is kind of all of that, but more refined. Despite being an all-BA design, it has real punch and extension. So that won me over. Truth be told, that’s still probably closest to an ideal tuning for me.
In a way, I feel like I did pick MEST MkII–that’s the one I went custom. I have eyeballed A12Ts for a while, but the U12Ts are so small and light that I have no trouble wearing them for extended periods; I haven’t quite felt the need to go custom there yet.
Here’s the bottom line: U12Ts are probably a safer bet, in that what they do is objectively good. They have both the superb bass implementation and the air that you’re seeking, and they’re universally lauded, as far as I could tell–I never found any negative reviews, and they rank among the top of many reviewers’ picks.
MEST is a wildcard. What it does is exotic and exciting. Both OG MEST and MkII have flaws or peculiarities that I can nitpick, but in the end I don’t really care, because they let me experience music in a totally different, intoxicating way. The plusses more than make up for any weaknesses.
I personally cannot stop reaching for MEST, and I know I’m not the only one so attached to them. But I also firmly believe that preference is a more important factor with MEST than with U12T.
I’m sure that doesn’t make the decision any easier. Perhaps price might–MEST is considerably cheaper, though I have seen sales recently on 64 Audio gear that would push U12Ts closer to MEST prices.
Silver lining: both are exceptional and well-loved IEMs; it’s probably easy to flip either if you don’t like one…
