What tunnel method for dynamic ip wan ?

Both VPN server and client are MT machines.
Client side have a dynamic public ip address and is behind ISP router NAT (MT and ISP router connected together with 192.168 class, public IP transparently natted)
What’s the method for site to site VPN , giving less headache as possible because of NAT presence ?
Thanks.

any tunnel capable of nat traversal will do: sstp, ovpn, ipsec, …