To your personal page first. But it is not written in stone. I am waiting until I hit 2.5K and I will be doing invitation only in my publication because I will be targeting a specific audience as well.

I'm not doing a submission page or post when I do and I will have my own domain pointing to Medium. Medium has instructions on how you can do this with your own www.thisismymediumpublication.com instead of gottamediumpub.medium.com.

Invitation only seems like less work.