Mixed! Our original flock, of six pullets, was a mix of Buff Orpingtons, RIRs, and EEs. The next year, I got 12 Ayam Cemani eggs shipped, got 6 to hatch, and kept 3 pullets. That's who we have in our "big girl coop" right now.
This year, I ordered a mix of Silkies and Seramas, 11 total, which I got at the end of March. I ended up with 14, got an extra Serama and two bantam Wyandottes as well. We lost one Serama and one Silkie, so our total of "littles" is 12, 7 pullets and 5 cockerels. They're just about 20 weeks old now, and we are finishing up a bachelor coop for the boys. Hopefully it will work out, I do love my boys!
I can't see myself ever deciding on one breed, or even a few. I love all the ones I have, for different reasons. The big girls are so funny to watch and give us lots of great eggs. I'm thinking of adding a couple of Copper Marans next year to get some more egg variety. The Silkies are so funny looking, I laugh just watching them doing regular chicken things because they look like muppets in my yard. And the Seramas are so tiny and friendly. I'd love some bantam Cochins!
We don't sell eggs or birds generally (the occasional cockerel), and I'm not intending to breed any of them any time soon. They're fun and they make me happy, plus my kids love them and also eggs.