I did L2TP/IPsec for mine since they are supported by default on iphone and android devices. Getting OpenVPN working on the iPhone requires jailbreaking, and android requires your phone to be rooted.
Plus, windows and OSX have native L2TP/IPsec support.
As a side note: If you have an android device running ICS (I assume JB works as well but I don't have any currently to test), you can run OpenVPN for Android
This presents a nice frontend to OpenVPN and doesn't need root.
Key points from the description are "Uses the new VPNService API that requires neither Jailbreak nor root on your Telephone." & "Only tun mode support (Sorry no tap, with Android 4.0 only tun can be supported)."
Plus, windows and OSX have native L2TP/IPsec support.