Ill start with my favorite Opening is Guilty Crown Opening 1 (My Dearest - Supercell) and favorite ending is Black Bullet (Tokohana - Yanagi Nagi)
hmmmmm for me its Fullmetal Alchemist END 1 (Nana Kitade - Kesenai Tsumi), Tengen Toppa Gurren Lagann-Sorairo Day opening, Death Note Ending 2 (Maximum the Hormone- Zetsubou Billy), The Trigun opening. I have so much but those are the ones I can think right now haha
Katekyo Hitman Reborn! Opening 4 "88" by LM.C
Mob Psycho 100 ending "Refrain Boy
Full Metal Panic Fumoffu Opening-Sore ga, ai deshou! and for endings I would go with Every Heart Op 4 from Inuyasha.
Orphan's revenge opening 1
Death note ending 2
My favorite opening is probably Unravel from Tokyo Ghoul season 1, there's so many good openings but that would be mine if I had to choose. As for my favorite ending song, it would probably be the ending for FLCL, "Ride On Shooting Star" by The Pillows.
Favorite anime opening: boku no hero academia s2 op1
Favorite anime ending: trickster ending 2
Shinsekai Yori ending 1
honorable mentions for the ending of hellsing (Mr. Big, Shine ;)
Kuzu no honkai
both the opening and ending for youjo senki <3