My favorite song changes with the seasons, to be honest so I don't think I could give an all-time favorite because I get bored of songs really easily. The one that popped in my mind though was "American Pie" by Don McLean. Not because I listen to this song, but because it has the nostalgic factor and happy memories with it

Other honorable mentions though:
Million Words by the Vamps
Mittens by Carly Rae Jepsen
Walking by VIXX
We'll Never Change by TXT
身后 by Spacex (yes there's a Chinese singer with this penname)
Love Wins All by IU

I am always open to song recommendations or sharing my own recommendations though!