Surflan is most likely the least toxic towards seedlings and safer than Colchicine which is even more toxic towards sprouted seeds.
It just depends on if you can git one or the other cheaper and don't mind following all the saftey codes if your decide on colchicine. I can't say if one is better than the other I supose it would also depend on if you are doing plant tisue or a sprouted seed. I think I would go with the Surflan.
Nigel the little fellowers are coming around for you, I hope that they are all polyploids it would be nice to see how they all turn out, I have been thinking since I won't be doing a big garden with mostly super hots I would have room to grow a few mutations. I might try doing it with surflan, I was thinking about doing it with the moruga blend, but I don't have a enough seeds to do it with of that variety. I do have enough seeds of the yellow brain strain and C. praetermissum that I have and they would be all this years seeds. It would of course depend on how well I feel and if I can do it at the right time and not in late fall. I( think it would be a great project for me to try, that would give me something to do other that just sit on my ass all winter.