Ages ago I worked for a while on OpenBSD on an old Dell laptop. It was a very stable system, and I could not complain. As previous posts point out, it tends to have good support for old hardware. I used Firefox for browsing, and it was noticeably slower than on Linux. It really depends on what software you need for work. If you prefer a BSD, FreeBSD tends to be more desktop-ready in my experience (but probably less secure in depth).