Which band is the most unknown out of all the ones you listen to? Keep in mind this is relative to you. Also, no bands that only you, or anyone close to you could possibly know of (friends' bands and of the like).
For me, it would have to be Kongh, a swedish doom/sludge metal band that has no songs less than 10 minutes long. I got their album from my dad who, on a business trip to sweden, went to a metal store and asked for recommendations from some kid there of albums to bring back for me and my brother.
I could also say Ocean Chief, of the same genre, but I don't actually own an album of theirs. Just a split album with Kongh that I bought recently.