Since I listen to like 90% anime and game soundtracks this is a bit tough, especially when there can be several artists included.
5: Shoji Meguro, mostly from his amazing Persona 4 soundtrack music design. It takes a special kind of awesome to make Reach Out to the Truth work as a lyric based Engrish main battle song loop that has only two short verses and a chorus. It honestly does not get annoying despite 50+ hours of gameplay, how I will never know.
4: 3 Inches of Blood, I have to add them since my username is ripped from one of their songs. Advance and Vanquish is their best album by far and I think anyone else would probably agree.
3: Junpei Fujita, AKA the guy who did the background music in Grisaia No Kaijitsu, not all of the soundtrack was done by him but all of the generic non unique songs that play often to set the mood of the scene were done by him. When I first got the soundtrack, I could find the songs I wanted first time from the track list without even knowing the name of the song, they just felt right and to me that speaks volumes on how quality the songs are. Orange Sunshine feels like Orange Sunshine like it could have no other appropriate name for example. I would post it but it looks like the anime industry threw another hissy fit at random and copyright takedown'd the music off Youtube. Thanks mediocre at best anime adaptation.
2: LiSA, I find all of her songs crazy fun for some reason, there's something about her voice that's so energetic.
1. In terms of sheer technical skill, whoever composed the entire soundtrack of Devil on the G-String takes top spot. It's credited to tiko-u on the soundtrack. They took inspiration from classical music and created a soundtrack based off old classical music but elevated them beyond mere covers or remixes, they were clearly their own songs that work independently but they were clearly based on existing works.
Others would be Iron Maiden, not everything they make is amazing but I can sit through any and all of their songs whenever they come up on shuffle without tabbing out and skipping it. Considering they have several 7 minute slow paced marathon songs that's impressive. Queen, I haven't listened to Queen intentionally for years but they're still freakin' great, GARNiDELiA their songs are good but Ambiguous blows all of their other songs out of the water. That Kill la Kill opening yo', the Umineko No Naku Koro Ni soundtrack has like 5 artists minimum but Dai is credited to my favourite ones (Hope, Happiness of Marionette, Revolt and Dir among others) and i've got the entire soundtrack on repeat right now. Though ZTS did the intense 8 minute extended battle songs that are pretty damn good on their own.
I'm posting Happiness of Marionette actually, it's my new cheer up song.