I can't say "most" -- different times of life, such broad tastes, etc. That said, I'll have a stab at two:
Television's debut album, Marquee Moon. I was 14 years old when that came out, obsessed with Prog, mostly. Gave away most of my lps. I still liked Pink Floyd and King Crimson from the prog bands, but that was all. (I won't say I didn't get into a lot of music that doesn't hold up, too, but really it changed listening habits in a large way, both with later bands and earlier bands).
Bill Frisell -- I was interested in jazz already, but was such a guitar freak, and here was the most original thing I'd heard coming out of a guitar. This is what got me deep into jazz from Ellington and Monk through AACM and on and on. The Paul Motian Trio is still one of my most listened to bands, and has some of my favorite Frisell work. Unlike Television, I kept returning to the records ("In Line" and "Rambler") with a furrowed brow. Kept taking them off because it wasn't quite getting me where I wanted to, but I kept having to put them back on a minute later just to check my hearing. Two weeks of this silly ritual daily, probably, before it clicked.