There's no magic here; either will do.

If it were me, I'd pick up the phone, but I'm old-school.

Something like "Hello, my name is temp9900-- I'm the guy who created XYZ. Do you know it? I've been thinking about the future of the site, and I wonder if you'd have any interest in buying it outright. I have NN subscribers, and generate $XX revenue each month on expenses of $YY, and I currently sink about ZZ hours a month into it. Interested?"