Pick a mirror
Any of any of the three works, but here is how to choose.
The reference/mirrors page lists the three onion addresses currently in the Anubis Market rotation. All three resolve to the same storefront. Your account, balance, orders and messages appear identically on any of them.
How to choose
Pick whichever opens fast. They are equivalent. If one stalls on the anti-DDoS queue for more than two minutes, try the next. Tor circuits vary across an evening, so a slow first attempt does not predict the second.
Older mirrors tend to be faster
Older mirror addresses have accumulated known-good routes through Tor guards and tend to load with less friction. The first entry in the reference list is the oldest and usually the fastest. Newer mirrors sometimes bounce for a day or two while descriptors propagate.
Bookmark, do not memorise
Do not type an onion from memory. Copy from the reference page. Or, better, bookmark the reference page inside Tor Browser and copy from there every session.
If you use the market more than once a week, bookmark one mirror inside Tor Browser as a shortcut. Just check the reference page monthly to make sure your bookmark still matches the current rotation.