It depends on your needs, mostly. I prefer ahrefs because their backlinks database is huge and superior to other tools. If you’re planning on doing a lot of link outreach this is a big advantage, plus your competitor analysis will be more accurate than if you used tools like semrush or seranking. Ahrefs falls short in its lack of decent reporting, in my opinion.
If all you want to do is track your rankings seranking is a great choice. The monthly price is low (compared to semrush & ahrefs), the UI is intuitive and the reporting is top notch. You can build out your own custom reports to fit your needs and brand. Their keyword research and backlink tools, whilst not as fleshed out as ahrefs & semrush are great additions and work well. For a budget option seranking is terrific.
If you’re running paid ads, managing social media AND doing SEO then semrush is the best bang for your buck. It’s got tools to manage all of that and the keyword analysis is the most accurate.
Ahrefs – If you’re focused on SEO and want to perform accurate competitor research.
Semrush – You’re interested in running paid ads and social media marketing, in addition to SEO – this tool has it all.
Seranking – Budget option which has good rank tracking and reporting. Can do everything, just not as good as the big guys.