I've never got the ToB fan's argument that this improved fighters. Fighters still exist, they didn't get improved, rather a bunch of bizzaro martial adepts showed up who weren't fighters in any sense of the word.
I thought the argument was ToB offered good
replacements for fighters and/or other existing martial classes.
If the word 'melee' characters were opted instead of 'fighter', the argument would have more meat...
I'm pretty sure that's what was meant.
If I had to pick a best I'd have to say the AD&D DMG.
My favorites by edition are:
AD&D - the Trinity (PHB, DMG, MM).
AD&D 2e - The Complete Bard's Handbook (no, I'm kidding), Faiths and Avatars (even though I'm not a big Realms fan).
3e - Arcana Uneathed, The Book of Nine Swords (it offers some excellent replacement fighters!), the Tome of Magic.
4e - none that I own (I liked the system, I don't like the way it was presented).
As for worst... most of the 3e-era splatbooks, particularly the ones with all the repeated material.