So far, OpenVPN has been working very well for me. Unfortunately, the iPhone doesn't have (yet?) an OpenVPN client, so I'm forced to work with what's available.
The options are: L2TP, PPTP and IPSec. If you were to install a VPN endpoint on CentOS, which protocol would you prefer? The condition is to avoid shabby VPN servers that make the system less secure. I've seen some PPTP servers for Linux in the past but I was not impressed with their security track record. I'm not necessarily talking about crypto, I'm talking about the way the application is written.
Another condition is ease of installation. I will compile from source if I have no other choice, but I'd rather avoid wasting time with that, as I'm quite busy with non-tech things nowadays. If the application is in a repo somewhere, that would be perfect.
Thanks!