The Anritsu has the best specs, lower noise floor, more dynamic range, lower RBW options, but I wouldn't really bother with the Tek or the Anritsu, personally. The Advantest is at least smaller, color, and more recent... not exactly a top performing unit (and similar vintage full desktop analyzers rather than that one which is advertised as a portable unit have better performance at a similar price), but the most modern build of the three and there should be plenty of parts available in the event there is an issue, those analyzers and their higher bandwidth variants are pretty plentiful on the second hand market.
What's your budget and use case, though? If portable is a actually important, Anritsu is sort of the top dog for handhelds but there are some lesser known Tek, Agilent, and other company analyzers that didn't have a lot of products and can be found for a reasonable price. If you're looking for a benchtop unit, Advantest is probably the leader for performance per dollar on the used market, and you can often get 8GHz of bandwidth for well under $1000, which is effectively unheard of for other vendors aside from older CRT and no DSP based units. If you're looking for specific signal analysis options or a particularly low frequency end, that could be relevant too.
Yes, Advantest is not likely to have much in terms of service manuals (though check KO4BB, there are some), but that doesn't mean they're impossible to service, and parts units can often be had pretty inexpensively. If I were in the market for an SA on a budget, I'd try to figure out my requirements and preferences (do I want a lot of bandwidth? Lowest noise floor? Hardware demodulation? Which is most important?), establish a budget, and see if at all possible, I could find a unit with DSP. Even a good older analog SA will have less dynamic range and a higher noise floor than a more modern SA leveraging DSP. I always prefer having something with an LCD on my bench too.... even big ones tend to be lighter and smaller. Of course the older CRT based analog analyzers are an option, and while you can get a good brand name and service manuals, but you miss out on some features, performance, and bench space.