I started with Purple. Overall, that album is the least consistent but contains some of their best songs, I would recommend starting there. After that, I listened to Yellow and Green which is my favorite. The Grey and Gold came out, so I listened to that one next. I think the mixing is actually fine on that one; it fits the overall sound well. Red and Blue are more “sludgy” than the others, so more of an apples to oranges but are still solid records.
Their newest release Hushed and Grim was the one that got me into them; I recommend checking that one out, especially the first 5 songs and the last 2. Really solid recent release. I also love Remission, it’s probably my favorite of theirs but it’s more sludge and I love sludge.