Man. TOP'S "BTO" is a great album, no question. So is ABB'S Fillmore Concerts. Really good choices. As is Floyd's ubiquitous "DSOTM".
But for me? When it comes to this list? Santana's "Moonflower" typically holdsat #2 to Steely Dan's "Aja" at #1. I have "Abraxas" on SACD, and it is quite possibly THE definitive Santana album. However, I like the different flavors on "Moonflower" (as well as the studio/live mix of tunes) and consider the live version of "Black Magic Woman" that appears on it to be the best ever recorded, and that goes up to present day. And I've heard LOTS of live versions of that song. My opinion.
But as always, it's: "Aja" for a million dollars, Alex!