palemaster is just for straight wizards, giving up some spells for some interesting abillities (better summoning, grafted arm, armor, etc.)
the TN is a multiclassing Wiz/Cleric that's very good at raising people. It gets some abilities (such as horrid wilting) either a level behind or the same level, to keep him or par at least a bit with straight casters, but he lacks many high level spells he could oltherwise have.
For giving up these things, the TN gets a lot of nifty abilities. He gets the +1 caster level for BOTH caster levels, allowing more undead to be raised (cause it's based off caster level and not character level, and hey! you have two caster levels) and more, albeit lower level, spells. They also upgrade their summoned creatures, and get things like an aura of descecrate, pretty much making their undead always get the benefits of descecrate as long as they're within...40ft.(?) of the caster.
The Cleric undead PrC is the master of shades, which is simply good at summoning incorporeal undead, instead of specializing in controlling them.
So, if you want to go powerful spells, go straight caster and just use necromancy spells (or master of shades, as you only lose 1 level of casting).
If you want to be the MASTER OF THE UNDEAD MUAHAHAHHAAHAH, I'd go with the TN.
If you like the idea of free undead and some cool undeadish abilities that don't really help the army, or you just don't like wasting wizard levels on cleric levels then go with the pale master.
The MoS loses one CL, the TN loses 4 per class (be ready to invest at least one feat in practised spellcaster, if not two), and the pale master loses 1,2, or 3 over his campaign as a palemaster, I'm not sure as I don't have the book on me at the moment.