If you are looking for the best SEO auditings like Keyword research, On page seo checker, Backlink audit etc. Then you should go for SEMrush. It is one of the best SEO auditing tool for you site. I am using it from last 2 years. I find it really good because of it's features like:-

1. Keyword Research
2. Competitors research
3. Organic Research
4. Position Tracking
5. Site Audit
6. Social Media Tracker

Thanks