I've got the monster books for both and the Everquest RPG PH.
The Manual of Monsters is 3.5 has a lot of undead templates and variants of D&D creatures (different kinds or takes of gnolls, trolls, treants, chromatic dragons, etc.) plus some unique ones (panda men, their nagas are neat reptilian fish men, some boar men like 1e MM orcs and a whole demon scheme). It also has some hugely high level bad guy NPCs, demonic, undead, etc. The art is good and the mechanics are mostly decent with a few hiccups.
Everquest is a variant of 3.0, it has things like poison and spell resistance which suck up damage from those types of damage sources. Monsters of Norrath and Monsters of Luclin provide a range of D&D standards some with twists (orcs, dark elves, skeletons, dog-like kobolds, spellcasting eye tyrants, etc.) and new things (frog men, four armed giants, etc.). Most of them have stats or variations for different level ranges usually with different tribes etc so you could have goblins with 1 hd then orange clan ones with 5hd then red clan ones with 10 then purple nightfang ones with 20 HD. Also some have stats for ones with class levels already (I know the four armed giants do).
Monsters of Norrath is full color, Manual of Monsters and Monsters of Luclin are black and white.
I like monster books and I have enjoyed and gotten use out of all three.
Everquest PH provides different races and classes and magic and feats and even d20 progression options (customize what you get each level through a point system instead of feats every 3 levels and stats every 4) and do iteratives based on weapon speed rather than everything being +5 bab. Races are strong with big bonuses and some using xp penalties instead of LA, but I like that dwarves are size small with a bonus to strength. Cat men, trolls, ogres, hulking barbarians, different dark elves, and advanced high int human types add to the race options while classes include things like a full BAB less mystic monk, shadow knights, full classes for enchanters versus magicians versus necromancers, plus shamen and the standard knockoffs. Some classes use nonstandard d20 progressions such as rogues using a 4/5 BAB instead of 3/4 or 1/1. Magic works on a point system with 8 readied spell slots and spells being individual to class lists and their point costs not tied directly to level while points are tied directly to stat bonus x level.
It is worth checking out but I don't particularly care for the magic system, I dislike point resource management and it drives incentives hard to maxing out spellcasting stat through race selection and point buy stat specialization. I like a lot how their rogues trapfinding is an autocheck when near traps and some other bits and pieces.