http://dark.lambdaplusjs35padjaiz4jw2fugdoeutse262phqr72uf634s2wdbqd.onion/meta/20495
If we go with tripcodes, an obvious choice would be to go for compatibility with the original ones created on 2ch (now 5ch after the hostile takeover). A disadvantage is that it's possible, although a tad expensive, to bruteforce those. Another option would be compatibility with Lynxchan, which does its own thing.