Which SEO tool has the best database?

I've used a bunch of SEO tools across a very broad range of industries, niches and topics. For both purchase-intent keywords and long tail, informational keywords.

I've noticed there can be a huge discrepancy between tools - specifically Ahrefs and SEMRush. Google Keyword Planner can be ok but I don't rely on it.

What Keyword research tool do you use, and why? Where do they get their database from? (To my knowledge, all SEO tools purchase search data from 3rd parties, namely those little browser add ons that 'reward' you for search).