what is the difference between PPTP and L2TP?
I think you should google it, much information is to be found. I can start of with this:
In terms of security, PPTP is obsolete. Only use with very long passwords (20 + characters) and not for matters where security matters.
Is sometimes blocked by corporate firewalls. Setup is very easy.
IpSec in conjunction with L2TP is a fair bit harder to configure and in general does not like NAT (there are workarounds).
Currently, it is the most accepted for companies with SSL VPN’s gaining tracking.
As for differences with more details, you will have to be more specific with your question (that is why you are getting few answers).