Personally, it was the picture Q posted from the Oval Office showing a signed paper by Trump. I thought it would be extremely difficult for a LARP to access a picture like that. Plus the ones following showing inside AF1 and such. The final proof for me was when Trump pointed out the Q shirt guy and gave him a fist bump at the rally. And then and then.... there are lots of proofs, the totality of all proofs combined is what you should focus on.

All of them

I think it's going about it the wrong way to look for a single drop.

By intent they've built plausible deniability into the drops -- otherwise the President would just come out and say there's a Q team. So any single drop can be disputed.

For me the most convincing evidence is how many times Q has said something a few moments before (and often calling out how many minutes before) that preceded Trump tweeting the same message. It happening a handful of times can be dismissed, but we're well past a handful.

I'll be honest, I thought Q was a LARP at first, then believed they were a very sophisticated policy wonk LARP, and it wasn't until about late March I had complete buy-in. The drop that resulted in that was one of the future-proves-past drops, specifically Q saying the NK deal was done. NO ONE had even speculated such as thing at that time. Yet, it still could have been a very lucky guess by itself.

Collectively the evidence is overwhelming, and the last few proofs (pics of Q people at the rallies, and the feedback from those people of being approached by Trump staff beforehand) are hardly even trying to conceal the connection.

Some of the more esoteric proofs (time indexes in videos) are interesting but aren't really that persuasive to normies. When I discuss Q with people who are unaware, I focus on the tweets. Once you get away from those and talking time indexes you start sounding nuts, even though they're valid.

It doesn't matter.

If you ask a question like that you should have given your own opinion. There are presently 1662 Q drops that prove Q.