Hi,
The VPN method to be choosen is fairly depends what you want to achieve.
The SSL VPN is slightly different from IPSec (with or without L2TP) VPN as it is working on application layer instead of network layer. There are few types of that from the client point of view. The question is again what you want to achive (full netwrok access or just few internal IP/port or just HTTP server on the LAN etc.). L2TP is mainly used on the access infrastructure such as xDSL or with dial technology. In respect to Windows I have seen such problem when the client is behind NAT the IPSec tunnel was unable to build up, because the built in IPSec client of Windows XP is only capable to run in transport mode where the NAT is not possible. If you use for instance Cisco VPN client the NAT is not problem.
Hope it helps, rate if does
Krisztian