I have a couple of SOL's (and 3 PSP's... sue me). I haven't made any changes except to add MicroPur tablets. In all cases the SOLs (or PSPs) are the nucleus of a larger modular kit, and so I think the things that are in there by default are adequate.
That said, I do prefer the PSP and its contents. I think it is targeted at an audience that has more skill and experience and can therefore use its contents to accomplish more. The SOL seems to be targeted at novices and several wilderness survival essentials (fire, shelter, signalling) along with the all-important positive mental attitude (both by having some useful gear and maybe getting some fishing in). I have the SOLs mostly because the local stores that carry AMK merchandise don't bother to carry the PSP.