Sonics matter to me, yes, but the Boulez is the only one I like of the conductors you mentioned. Sorry, but I don’t really care for much of Bernstein’s Mahler, I don’t like hardly any of Solti’s Mahler, and the Ozawa M7 is actually very good but the bells and cowbells are inaudible at the end (a very important aspect of Mahler’s orchestration). The earlier Bernstein M7 is one of the few Mahler recordings of his that I like, but it’s not a top choice for me. He wallows too much in the Nachtmusik movements (ignores their tempo suggestions), and screws around with the score too much.
I have a preference for less conductor-involved recordings, which is why I don’t like Bernstein and Solti and why I prefer people like Boulez. I prefer when conductors stick to the score, and a cohesive structure and textural clarity matters more to me than emotional impact. In other words, I get enjoyment out of hearing all the details. That’s how my brain works. Plus, I’m a percussionist so yes, the bells, cowbells, and tam-tams matter a great deal to me.
I’d argue that Boulez, Vänskä, and Zinman make more sense of the symphony’s structure than Bernstein does. I’d also argue that the Fischers, Vänskä, and Boulez have far more textural clarity than the recordings by Bernstein, Solti, Ozawa, and Haitink, but that may have to do with sound quality.
Preference is all subjective anyway. Sorry to hear you don’t like Bloch’s M7.