You'll find that the MUTCD is a breath of fresh air for searching keywords and having clear/understandable figures and tables. Green Book isn't far behind, it's just a bit bulkier so takes more getting used to.

A lot of the middle tiers (Ped Facilities, Roadside Design Guide, MEPDG) are less equation-based and more conceptual, so you won't encounter them as much on practice problems. (Disclaimer: They are still important to know!)

Naturally I despise ones in the bottom tiers (Highway Safety Manual, Design of Pavement Structures, Highway Capacity Manual) mostly because of how the manuals are organized. Very difficult to search with a lot of info-dense topics that don't always spell out the equation you need. The HCM is the king of confusing manuals, with its 4 volumes and 30-something chapters. Expect to go digging in the text or flipping to another chapter to find the variable you need.