The hard thing about SEO tools is that the best one for you is the one you'll actually use and get value from, which depends on your situation.
At the high end are Ahrefs and SEMrush. They are expensive but have a ton of features, though it can be overwhelming. If you have a dedicated SEO person, then maybe this is worth it.
However, if you're like most stores and are doing it yourself, then I'd recommend starting smaller. One of my favorite simple SEO tools is Siteguru. I like it because it's simple and actionable, but especially because they have a lifetime deal via Appsumo. I got a $40 lifetime license on Black Friday. They may still have a lifetime deal on Appsumo.
Using Siteguru my initial site rating was ~30/100, and over the next few months, I got it close to 100. They give you a simple to follow to-do list to fix site issues like missing tags, broken links, etc. that I chipped away at a little every week.
If Siteguru doesn't still have a lifetime deal on Appsumo I'd recommend looking for a similar lifetime deal so you're not spending too much.
Then, once you use the cheap, simple tool to the fullest extent and want more, then you can pay for one of the more expensive tools with a lot more capability like Ahrefs, SEMrush, etc.
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