(I'm presuming you mean IPsec tunneling, not just IP tunneling)
A quick rundown is:
IPsec is more or less considered the standard by most network hardware vendors. It's quite a bit more complicated than OpenVPN, and tends to be a bit faster, as it runs in kernel space (network level).
OpenVPN is an open-source project by James Yonan. It's based on SSL/TLS, is arguably much easier to configure, but runs in user space, and thus tends to have more resource overhead as a result.
The above summary is from a nice Linux Journal article from January 2008 comparing the two. I recommend reading it, as the author (Rami Rosen) gives you a good background on the tech and provides examples of each in use.
http://www.linuxjournal.com/article/9916
I rather like OpenVPN, myself, and use it on a nearly daily basis, but we also have to use IPsec for many things at work with Cisco gear...