[Freesurfer] BEMs

Hi,

I am doing EEG source localization, and I am trying to understand the resulting differences between the watershed algorithm and the command mri_make_bem_surfaces. I know that the watershed gives me 4 surfaces (brain, inner skull, outer skull, outer skin) and the mri_make_bem_surfaces gives me 3 surfaces (inner skull, outer skull, outer skin). But, which of those two will give me at the end of the day the most accurate source estimates in EEG? And also, do I need some special MRI sequences to obtain those BEMs (i know that in the case of mri_make_bem_surfaces i will need to process the flash 5 synthesized sequence, but is this the same case for the watershed?

Any comments and advice are strongly appreciated.

Thanks,

Camilo