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.

I was myself in the same situation and decided for NEXUS because I like the way Scrum.org does things.

Since all them aim to do the same thing,Why not choose one that comes from a creator of Scrum,that adheres smoothly to Scrum itself.

I read a lot of criticism of SAFe(very superfficially can´t give an opinion) ,and did not like the Less made your course and receive your certify and Don´t forget to send us money ervery two years way of doing things(Reminds me Scrum Alliance),and I have seen myself the quality and compromisse that comes from certified Scrum.org Scrum masters.

So the stack SCRUM+Scrum.org implementation of Kanban+Nexus made total sense for me.

And of course studying all them together makes getting certified easier. 

Learn Spotify model. Many organisations are sick of SAFe or LESS, both having lots of deviations, and implementing it. Also it fits with Scrum perfectly.

At first I did not like the concept of SAFe,too many things,that Scrum.org addresses with smaller initiatives. easier to implement.

As I understood Safe "would be" NEXUS+PAL+EBM.

After read about SAFe it is just no Scrum.

One can wonder if it violates the agile manifest itself or not,but it is definitely not Scrum.