Tools depends on the size of your client and the specific needs. I can find use cases for Stat and I have clients that are no where near big enough for that tool and an basic SEMRush subscription would be more than enough to get them off the ground.
If you have 1000USD for SEO tools specifically other than Ahrefs and Semrush ( strong tools) I would suggest getting SIMILAR WEB PRO. They have amazing data that you can do more beyond those two. Sometimes you want to look at data outside your organic search to get a better indication, you will be amazed with that how having other data such as sources, regions and so on can further help with your SEO decisions
It’s an indispensable tool for most of the SEO process from the first steps to the last ones. From research competitors for the SEO strategy to External SEO, Outreach techniques, like Link backlinks search. And many other useful SEO buns.
I’d think about Screaming Frog also because it’s a necessary thing for the Internal SEO and metadata.