If you get some spiders bite poisons and fabled ghoulbane you will plow through undead as a pally. Along with instrument of nife making you pretty much the highest DPs vs undead till about 60-65. Then again it's not easy finding people selling poisons for low levels. And unless you are on fv fabled Ghoulbane isn't available.
This is kind of a misguided queston... what does "best" even mean? Solo or group? High end content or mass killing light blues? Regardless the class that is best against undead is most likely the class that is best against any other mob type.
Grinding for experience and AA's when a group isn't available. So quickly killing blues and light blues.
Magician or necromancer then, as others have said, are far more superior at quickly dispatching undead (or live) mobs than any priest, and unless swarming, better than any knight. If you really want a class that molos extremely well, choose either of them, you will not be disappointed. Trying to take a character from 0 to 100 by yourself without being power leveled or drastically helped at all, either of them will do it 2 or 3 times faster than a priest or knight, that's how big of a difference it is.
Magician for sure. Necros get the same (some would say better) expo rate killing yellows/reds mostly, just slightly slower.
At the high end as well as leveling up Paladins can be fun for routing undead Your toolkit will include Snare Root Slow Nukes that Ac debuff Nukes that proc extra damage Slay undead Kill shot that boosts slay undead Pacify Fade Instant cast ivu Group fixed Ivu I'm sure I'm missing some Killing only undead can be rewarding from a fun lore perspective it also has a lot of fun dungeons to explore Lguk befallen unrest veksar the hole ruins of illsalin and the list goes on
