I got diagnosed late last year and I chose "mixed reaction both good and bad."
On the good side I felt vindicated, confirmed, and relieved to know for sure. On the bad side I felt angry that this didn't happen earlier in my life. I also felt strangely vulnerable and a little bit bitter. I felt "newly minted" and yet angry about that because I knew I'd lived with autism all my life and there was nothing "new" about it just because I'd finally got an official "say-so."
So, weird mix -- relief, glad to know for sure, also anger, bitterness, feeling vulnerable. I didn't even want to come here for a while because it can be rough here and I felt oddly fragile for a while.