Isotope with longest decay chain to reach a stable isotope

In a sense, this question is unanswerable. (Still a good question!) } Consider the natural decay chain of $_{92}U^{238}$. This isotope goes through 14 steps, along various routes, to decay to $_{82}Pb^{206}$. This $4n+2$ series is the longest naturally occurring one. See http://en.wikipedia.org/wiki/Decay_chain

However, someone could immediately claim that they have some $_{94}Pu^{242}$ which decays almost at once by $alpha$-emission to $_{92}U^{238}$. The someone jumps up with some $_{96}Cm^{246}$, and so on, and so on.

Just made a small Python that builds a graph from a "decay.txt" file I found somewhere. Longest path in it is:

Sg263->Rf259->Lr259->No259->Md259->Es255->Bk251->Cf251->Cm247->Pu243->Am243->Np239->Pu239->U235->Th231->Pa231->Ac227->Fr223->At219->Rn219->Po215->Pb211->Bi211->Tl207->Pb207