For me there's two main ones. Spurs and Man Utd.
Spurs for obvious reasons.
And Man Utd because being born and bred in London, when I was in school, no word of a lie, 90% of my year group supported Man Utd. You'd get one or two Arsenal fans and the odd Liverpool fan. And this was obviously a time when they were winning everything, the treble etc. Half of them didn't have a clue about football or couldn't name more than 4 players, but literally everyone supported them. So I naturally grew a major dislike to them. Its funny because the older generation, i.e. anyone born 2 years before me or more, all supported Liverpool round here, but they have suddenly only come out of the woodwork in the last few years, so I'm not too fussed about them. Although every local bar and pub was packed to the rafters with Liverpool fans before the pandemic for major games, just goes to show the amount of glory hunting Londoners about.
I wonder who the new generation support now, hopefully being in London, a lot of them are starting to support us.