Are we talking strictly rulebooks? If so...
OD&D-
Best= Greyhawk, despite the Thief and Paladin, it really opened up the game otherwise.
Worst= Blackmoor: God awful rules variants. But TotF and Steve Marsh's/Tim Kask's monster additions help it from being complete garbage.
Honorable Mention for Best- Original Holmes edited Basic Set. AD&D Monster Manual (this is a OD&D supplement, mechanically)
B/X/BECMI-Different games in their presentation of style of play , but I'm lumping them together for brevity
Best= Moldvay/Cook/MArsh B & X booklets. My fave edition of the game ever. Clear, concise, fantastic presentation of the ruleset.
Worst=Companion Set. Huge disappointment. Shelved, never used.
AD&D
Best= 1E DMG- as an in game reference, not great. As a work of DM advice and inspiration? Amazing.
Worst=Most of the bad hardcover books came out long after I had given up on D&D for RQ and other RPGS, so for early titles-Fiend Folio: Amazing cover that totally blew me away the day it arrived on bookshelves- Full of mostly crap monsters I never used.
AD&D2- I came into this later in it's life
Best=Monstrous Manual
Worst=2.5 hardcovers.
Dishonorable Mention=Tome of Magic
D&D 3.0
Best=Manual of the Planes (I tire of what has become of the Great Wheel post Gary, but this is a good read)
Worst=PLayer's Handbook. Like all WOTC books, here we have the beginning if the "lacks an Author's voice " problem which makes for a horrible un-inspiring read. Hate the presentation/aesthetic.
Dishonorable Mention= DMG. Horrible advice about making the game your own because everything is countered with 'you probably will break your game'. The Yeah, thats great, but... DMG. Only useful for full blown NPC stats and some magic items.
D&D 3.5
Best=I don't have a best here for rules. The only thing I still own is Secret's of Xen'drik
Worst= The entire 3.5 change. So PHB,DMG, MM.
D&D 4.0
Best= DMG 1. A DMG that's actually great at teaching a DM how to be a DM on the creative side (Some of which reprinted in the 5E MM) , and at the table, and tools you need.
Honorable Mention=Monster Manual 1. For finally making all the boring monsters interesting in combat, all the samey monsters different in combat, and self contained stat blocks. Yay! I'm fine with the minimal fluff. I grew up with OD&D monster descriptions. I also like the knowledge check mechanics to figure out the lore.
Worst=I prefer the Essentials changes in nearly every way, but in retrospect Monster Vault sacrificed it's word count too much in the direction of fluff. It sorely lacks a variety of creatures. Overcompensation.
D&D 5.0
Best= DMG. Solid guide for a DM on the creative side and the table side., good presentation of Magic Items, and nice section at the end with rules variants (could be bigger though, as implied through the playtest).
Worst= Monster Manual for it's huge step backwards to earlier edition non self contained statblocks which require referencing the PHB for spells, and removal of interesting monster powers/combat abilities in the name of simplicity (hint for WOTC , you can keep monsters simple in the stat block, AND make them interesting combat encounters, check out 13th Age Monsters for a textbook example)
Dishonorable mention=Volo's. In the buildup I figured I would be all over this. After spending roughly 2 hours with it, back on the shelf- it's like the Fiend Folio was for me in 1E, except I was smart enough this time around not to purchase it first.