(This is the post I accidentally deleted a couple of days ago, fingers crossed for this time)
Four years ago I wasn't reading any webcomics, today - about 30 that are actively updating, with a few more that are on hiatus with some hope of restarting. I've been meaning to do this for a while, but it's probably going to work best if I split it up over several updates (no promise when the next one will be).
Requiem: Huge Sfnal webcomic updating three times weekly over the past decade. Backdrop is a Celtic derived society that seems to have crossed over into another world sometime in the Classical Era. The plot evolves out of an initial coup attempt that reveals deep manipulation of society going back thousands of years, along with a separate?/interlinked? threat from the obelisk-like technology that predates humanity's arrival. The stakes are high as our heroes have uncovered evidence of at least one technologically-mediated near extinction event that had been erased from their history. Strong characters (mostly female) and good storytelling. Also probably the best art of any of the Poser/Daz based 3D webcomics, I use Studio and the amount of work that goes into putting out three multi-panel updates a week doesn't bear contemplating.
Project Skin Horse: Skin Horse is the black project charged with dealing with problems among the various non-human intelligences, zombie communities, intelligent swamps and whatever that get left behind when the mad-scientists lose interest (it's a spin-off from the mad-scientist oriented Narbonic). Our heroes include Sweetheart (talking dog and the team-lead), Unity (zombie killing-machine/patchwork girl), Tip (cross-dressing psychologist and lothario), and Nick, who is a black helicopter (he's actually the brain of a foul-mouthed gamer wired into the controls of a V-22), plus frequent guest-star Doctor Lee, who is the Korean-American mad-scientist who created Unity and Nick (she's also Nick's girlfriend). Often silly, but very well written. Updates daily.
Girl Genius: The 80-stone Hugo-winning gorilla of webcomics. Covers the adventures of Agatha Heterodyne and her friends as she attempts to reclaim her family heritage as the most feared of Europe's Sparks (mad-scientists) in a steampunk world. Well written and drawn, though with an unfortunate tendency to strip Agatha down to her bloomers more frequently than the story truly requires. Updates three times weekly.
Gunnerkrigg Court: The adventures of Antimony Carver at her new boarding school, the eponymous, and mysterious, and huge, Gunnerkrigg Court. I'm not quite sure how to categorise this - aetherpunk? - but bring your knowledge of myth and fable. There's noted art evolution, from okay-ish to perfectly passable and occasionally down-right gorgeous, but the writing starts out good and just keeps on getting stronger. Updates three times weekly.
Schlock Mercenary: Another Hugo Winner. The ongoing adventures of Tagon's Toughs, a group of space mercenaries, including the eponymous Schlock, who is a cheerfully homicidal 'carbo-silicate amorph'. Notable art evolution from its earliest days and the story-telling progressed fairly quickly from gag-strips to increasingly complex year long arcs (and there's an underlying arc we're told will see things come to an eventual conclusion). The Toughs have totally remodelled galactic society twice so far, and it looks like they're headed for a third time. Updates daily, and hasn't missed once since 2000... (but has a really good archive page!).
Freefall: This started as gag-scripts around an amoral alien and his stupid robot sidekick on a colony world where the robots outnumber the humans several hundred-fold, but then they acquired an uplifted female wolf, Florence, and it has evolved into a complex story revolving around Florence and the rights of AIs (and Florence is seen as an AI just as much as the robots) to be seen as sentient beings and own property, as opposed to actually being property. Updates three times weekly.
A Girl and Her Fed: If I had to pick a single comic as my favourite, this would be it. It splits into two books, the first is about the surveillance society, with the eponymous Girl (who we eventually find out is called Hope), finding out that she is on a terrorist watchlist and under surveillance from the eponymous Fed. Fairly rapidly Hope has things turned around so that she's helping the Fed(/Pat/Sparky) investigate what the government did to him and every other agent in his agency and why so many of them are now dead (quote 'We probably lost several future Presidents'). Along the way we meet Hope's best friend, Ben Franklin (yes, that Ben Franklin), Pat's best friend Speedy the hyper-intelligent Koala, and Ben Franklin's undead pixie army. The second book picks up five years later, with Pat and Hope married, Pat now running the agency and they and the other agents investigating a plot involving the rogues who weren't caught in book 1. The current art is fairly standard inked look, but the comic was originally done in a quirky black and white style (which I rather liked) and there is still a chunk in the middle of book 1 that hasn't been updated. Updates twice weekly.
(The AGAHF setting is also the backdrop for the author's Rachel Peng technothriller series of novels,
The Digital Divide and
Maker Space which are set between the two AGAHF books and involve the first OACET agent assigned to liase with the Washington DC PD. As Rachel is Chinese-American, gay, and, technically, blind, she's one of the most spectacularly diverse lead characters I've come across.)