I've got three!
Camp Weedonwantcha by Katie Rice. Gorgeous art and character designs, the story has made me tear up multiple times, and I've also laughed out loud many times, which comics with a storyline rarely make me do.
Also Rabbit Hole by Detrah on DeviantART. Phenomenal panels & design. Stunning to look at, and tense and suspenseful.
I really enjoy Zarla's Handplates comic, an Undertale AU. I usually don't get into alternate universe fan-comics (or any fan-comics, really) and I'm not even a massive fan of Undertale or Sans or Papyrus, but I really like Zarla's depiction of Gaster, and I'm a real pathetic sucker for hurt/comfort style stories, comics or fiction, where all you can do is pity a character or two who's been put through hell and gets the odd blanket for a reward.