Ahref & Semrush , both are a good tool, it depends on your goal that for what you are going to use the same.
Like I am using both the tool as per my requirements
AHREF : It is basically for Backlink Checker, Organic Keyword filter, Featured Snippet checker & Keyword ranking or explorer but not good for PPC or advertisement.
Semrush : Its is an all in one tool & I personally like this tool allot as it helps me in managing the report creating report dashboard as per my metrisc, helping in SEO based articles, and many more but most importantly for Ad copies & PPC here you can easily find that what your competitors are using in there ad copies which kind of creatives they are using & how they are performing