OpenVPN is much easier to configure for most people. Neither OpenVPN or IPsec requires much maintenance after setup, except the occasional certificate renewal in some setups.
They are not really comparable though. IPsec is much more efficient and scales significantly better, so there is a reason why IPsec-based VPNs is used for site-to-site in enterprise networks. IPsec is often used with GRE, alternatively used in VTI mode, so you get an interface and can run routing protocols over the links.
Personally I use IPsec for all site-to-site infrastructure VPNs for this reason, as I have full control of the equipment in each end.
With roadwarrior user access VPNs, where performance is not as important as within your infrastructure, I often find it easier to just throw in OpenVPN. The benefit is that you reuse the configuration method on all platforms. While IPsec is often natively supported by the OS, you have to find out how to set things up for each platform.
I do wish that VPN-providers you can subscribe to would provide IPsec tunnels though, just for performance reasons, but I can understand why they don't, thinking of all the support tickets they would get..