SPS or LeSS or SAFe?

If you want to explore something to potentially be able to advance your career and have mobility into organizations using other frameworks, I'd recommend checking out job boards to see what knowledge companies are looking for, especially companies in a particular domain, industry, or geographic area. That may give you a good idea of what skills would be marketable.

That said, Nexus (what the SPS tests against), LeSS, and SAFe solve different problems and aren't easily comparable. Nexus, LeSS, and Scrum@Scale are frameworks to give structures around Scrum to help multiple teams coordinate when working on a single product. Scrum@Scale also provides some guidance that could apply to portfolios or other parts of an organization. All three are strongly rooted in the Scrum Guide. SAFe, at the Essential level, provides structures for multiple teams to work together to build a single product, but, although it uses some of the Scrum terms and concepts, is not based on Scrum as it's defined in the Scrum Guide. The higher levels of SAFe also provide considerations for highly complex products, portfolios of products, and an enterprise that consists of multiple products and product portfolios.

I advise scrum masters to take the PSK - this is THE way to get you scrum team to be more effective.  I know it's not in the list, but unless you are scaling, the PSK is better for team and scrum master effectiveness.