For your own site, GSC is still the best free option because it gives you real data straight from Google.
For keyword research, Google Ads Keyword Planner is also worth using, especially for finding ideas and variations. But that’s for research, not true competitor tracking.
For other people’s sites, there isn’t really a fully free Ahrefs/Semrush alternative. You can get bits of data here and there, but not a full replacement.
So I’d say:
GSC for your own rankings, Keyword Planner for keyword ideas, and Ahrefs/Semrush in limited form if you want to peek at competitors.