Semrush

Semrush covers similar ground to Ahrefs — keyword research, backlink analysis, site audits — but is often considered a bit more approachable for newer users, with more built-in guidance and a broader set of features that extend into content marketing and social media tracking.

For a newsletter, the competitive research tools are probably the most relevant part: you can see what keywords similar newsletters or blogs in your category are ranking for, which is a useful way to find topics worth covering that are already proven to attract search traffic.