Everything has a use and pros and cons. Tunnel brokers you have to sign up but optionally also provide you with other tunnel protocols than just proto-41, which 6to4 also uses. The big advantage of a tunnel broker, depending on the one one picks though, is that one gets a static address and NAT-piercing if you select AYIYA, the more important thing though is that 6to4 is extremely hard to debug to the anycasted nature. 6to4 works well in quite some cases, but in the case that 'something' is broken it will be a huge pain to figure out what really is going wrong, which is especially painful when trying to connect to a host on the other side of the planet, in that case tunnel brokers, where the address space is managed and controlled become much easier to use. Also configuration wise it can almost not become easier than with AICCU or for that matter one of the TSP clients. See for a comparison of the tunneling protocols as each has pros and cons too.