Hard to narrow down just one single, but my favorite artist altogether has to be Porter Robinson. Got tickets to see him this weekend, super excited for that.
Just going through my library for other stuff I love and completely unable to narrow any of this down, in alphabetical order since I don't want to try and put a list like this in any particular order, and definitely forgetting lots more: 2 Mello, Alohaii, Avicii, Blind Guardian, Blue Stahli, Camellia, Celldweller, Daft Punk, Depeche Mode, Dragonforce, Dream Theater, Fatboy Slim, Feint, Foo Fighters, Fox Stevenson, Ghost, The Glitch Mob, HammerFall, Illenium, Inabakumori, Iron Maiden, Judas Priest, The Killers, Madeon, Maduk, Moe Shop, Mr. Bill, Mystery Skulls, Nirvana, The Offspring, Pendulum, Powerwolf, The Prodigy, The Qemists, Ronnie James Dio, San Holo, Snail's House, Sonata Arctica, Sponzi, Stessie, Synthion, TheFatRat, TOOL, USAO, Veela, Voicians, and Weird Al Yankovic.
I'm also the type of degenerate that listens to ridiculous meme mashup albums that keep popping up in my Youtube recommendations, to the point where that's all I know of more mainstream pop music. Shoutouts to Pluffaduff, Jazzwave, TCMusic, LibraH, William Maranci, Jake Ranney, Siivagunner, and of course Neil Cicierega.
For game OSTs, Chrono Trigger is the GOAT. Undertale/Deltarune has to be second. Jet Set Radio and anything else by Hideki Naganuma. The Word Ends With You. Them's Fightin' Herds for taking already fantastic tracks and doing some kind of Dynamic Music System witchcraft in-game.