Why out of curiosity? Just personal preference?
But what features or cabalities are you missing with Linux?
Android has bits and pieces of it, but not nearly enough.
Creator of the world's most used SSH implementation OpenSSH, the world's most elegant firewall PF, the world's most elegant mail server OpenSMTPD, the OpenSSL rewrite LibreSSL, and the NTP rewrite OpenNTPD. OpenBSD -- the cleanest kernel, the cleanest userland and the cleanest configuration syntax.
I mean, I love OpenBSD too, but you can't drink the Kool-Aid like that. It's got just as many design tradeoffs built in as any other competent OS.