It's hard to choose, there's just so many great songs. Maybe it depends on what you're in the mood in.
Right now, it's "In My Life".
And your bird can sing! Specifically the recording from Anthology 2 where you can hear John and Paul laughing
Ooof. This is like asking me to pick my favorite child! Probably something off of Rubber Soul.
I Saw Her Standing There
It's certainly not one of their many compositional masterpieces, but I really love this song because of how quintessential it is of that very early British pop invasion style with the catchy twangy guitar melody.
Pretty hard to choose, TBH. I'll go with 3:
Those would probably be my top 3 normally.
I never really listened to the Beatles that much, but for some reason Strawberry Fields Forever really resonates with me.
It almost feels like a perfect song to me, not sure why.
Sometimes it's I've Got a Feeling, other times it's Happiness Is a Warm Gun. The medley from Abbey Road as a whole is up there too.