I know it is subjective, but hear me out and understand why I think this fat that is USUSALLY trimmed from the ribeye steak before you get it. This is why i buy the whole USDA prime, prime rib roast. Obviously “prime rib” doesnt mean prime grade.
So here is a cross section of a prime rib roast.

(these are from amazingribs.com)
The “rib cap” (technically the spinalis dorsi) is the best meat on a steer and this is a widely held belief. You get your odd proponent of other stuff and I am a big brisket man but clearly this is the best meat. The other muscle (B) is the *Longissimus dorsi * and I love that also. I argue that that big blob of fat at the other end is actually the best fat. I thought it might be the fat separating them but in blind taste tests I ALWAYS picked the former. If you buy a standard ribeye this piece will have been removed as it is a “great big glob” and too much of it is gone to the burger.
Here are two uncooked ribeyes from different ends of the rib roast which goes from between the 5th and 6th down to between the 12th and 13th (as I recall). In a standard ribeye that whole fatty end gets trimmed away along with too much of the other.I know the intramuscular wispy fat might be the best but no way to taste that separately.
Finally, here is how the fat looks cooked up.
What is your favorite?