Ahrefs all the way. I am using it from last 2 years. Semrush data can be seriously unreliable. Their backlink scanners are a joke. I used to have pro accounts on both services, but last year I canceled my SEMrush subscription, moving to Ahrefs (and LTP) completely. I'm on their $350/mo plan and I cannot be more happy with it. The only thing that I don't like is their KD meter, which always displays a total BS.