OOOOOOOOOOOOOH, nice thread.
And really difficult question, as there are hundreds and hundreds of openings out there. And let's start by not using "best of all time" will we
Contrary to popular belief, I didn't watch many anime or read many manga, my knowledge is actually quite limited. But even if I didn't watch the media in question I still spend enough time on youtube to know many of them.
Now when it comes to opening quality, we need to know exactly what we're talking about : the music, the imagery or the general flow created by both ? When I judge an opening I tend to take into account that last one, as sometimes I love the song but the imagery is bad, which prevents me from liking it to its fullest, or the contrary there is some slick animation but the song is not that great.
You named quite a few legendary openings.
Guren no Yumiya is one sick opening indeed, it throws you directly into the general atmosphere of the show, and even if we follow a quite repetitive rhythm line all along there are enough variations over it to get hyped (the fact the animation is top-notch helps).
Tank from Cowboy Bepop is certainly one of the best, I mean, which criticism can we make, really ? The animation's there, the song is great, uncommon for japanese anime and it has a wonderful mood.
While
Again is not my fav FMAB opening song (it's the 4th), it is indeed the best opening. The music and animation fit
perfectly together and the creators had some impressive ideas (ie, Winry being jostled by the wind after a scene where Ed and Al lost their respective body parts, a nice way to show she was affected by the events even if she didn't participate in them directly).
Everyone knows
A Cruel Angel's Thesis obviously, but while it is indeed a legendary song, I don't think the opening in itself is that great. Rythm of the animation follows the music, but all in all it's quite simple.
In MHA, I'm fucking in love with the song from the 3rd opening, Sora ni Utaeba. In terms of song + animation I think the second one is the best.
Among the recent openings, I liked these two a lot as they manage to score high in both components of a great opening in my mind.
Beastars OP1 (ALI - Wild Side)
This one is really original for an anime opening, whether it be because of the music or the technique used, and let's not forget the symbolism.
Dororo 2019 OP1 (Ziyoou-vachi - Kaen)
It's quite soothing for an opening, the music and the color theme create a nice atmosphere, which is accentuated by the great animation in the second part.
And I kinda want to throw in the
Yuri On Ice opening there too, I was so obsessed with it back in 2016 (omg already).
The first Fire Force opening (Inferno) has an amazing animation too with all the colors and effects.
When it comes to songs only, as I think it's the main subject of your topic, here's a list of some I like, heavily shonen inspired as they're basically the only op I care about lmao.
... and that's when I realize almost all songs I wanted to name are actually endings
oopsie seems like i went a little too far
