There has been some discussion on the viability of still using 6to4.
If you look at the list of 6to4 operators, you will notice that the list is actually quite long. Also, the list is incomplete, as there are actually more 6to4 gateways in the wild. In Germany alone IP Exchange GmbH (AS 15598), DFN (AS 680), Cablesurf (AS 35244), Hurricane Electric (AS 6939) are visible BGP prefixes at DE-CIX for 184.108.40.206/24.
Also, the claim that NAT is a huge issue with 6to4 is actually shown to be wrong because we are running 6to4 successfully in multiple IPv4-only locations behind NAT routers. So, just try it yourself. We have prepared a simple script which sets up 6to4 for you (Linux users). Windows/Mac come preconfigured with Teredo/6to4 tunnels. We have had mixed experiences with Teredo under Linux, and thus use 6to4.