I started with FreeBSD (Release 3.2 IIRC). After a couple of years I tried OpenBSD and since then I nearly only use OpenBSD.
I love the simple OpenBSD installer and the easy way to do a PXE install. Doing a FreeBSD PXE install is a nightmare compared with the simple instructions at
http://openbsd.org/faq/faq6.html#PXE
I still plan to try ZFS on FreeBSD though, but with only 1 GB memory in my fastest machine, that seems to be a no-go.
I installed NetBSD once or twice, but never had or made enough time to be become thoroughly acquainted with it.
Same goes for DragonFlyBSD, although I really would like to play with the Hammer file system.