I have been using ahrefs for years and I can't even imagine a day without it. From keyword research to link building, ahrefs has everything.
Unless you are building your own website and SEO is not important, then semrush would be a great choice as well.
Ahrefs is more geared for SEO as a whole, and gives you more data and analysis to help you determine your next steps; Semrush focuses on keywords, competitor research but not like ahrefs, Also now Ahrefs is very expensive than the Semrush.