I'm def down with sharing my all time favorite works on the site - calling things "masterpieces" is a bit weird but whatever - all of the things I've linked below are comics on the site that I consider worthy of studying & imitating.
I share this a lot - but it deserves all the attention it can get. The panel structures in this comic are some of the most dynamic and complex compositions I've ever seen in comics.
One of my favorite short series on the site - F&F's Black & White rendering is masterful and perfectly captures the campy horror-B-movie tone of the story.
I just love the aesthetics and color palette of this short, it's great, and the story is super cute too.
McKay & Gray are one of the best duo's on the site, this is their first completed series, the art is a bit rough but it's solid (their later series are even better in this regard), but the storytelling and characterization are absolutely wonderful. They also have a youtube channell where they share a lot of great comic-making advice.