Each tool uses its own formula so you’re always going to see some differences.
Some weight (seemingly too much) on the individual pages ranking, and will call a term easy even if its a bunch of pages on really high authority sites
(So a ‘weak’ page on NerdWallet, for example – still hard to beat given how massive they are in the finance space.)
I’d recommend checking them out, and sticking with the one that works for you.
I’d define that has some decent level of consistency in “With equal page optimization, I rank highest for stuff it grades as easy, lowest for hard, and in the mid group for medium”
– if you find one that aligns with a bunch of your intentional work like that, it’s a good sign that you can use their stats for ‘easy’ to go scoop up more easy wins.
What I’d likely do here is grab a bunch of terms, toss em into the keyword tool at ahrefs and use the ‘traffic share by domain’ report.
If you take a look at the top sites and feel like you can compete with them in terms of the amount of content and links, go for it.