Thaumaturge or Pale Master...?

[Nachti]

Don't they last for 20 rounds (or 40 extended) ?

Nope. Animate Dead lasts a long time. The downside is that they arent that strong, require much attention (click and attack) and a caster has to buff each one, resulting in lots of spells used.

[Rinzler]

You sacrifice CL for a Pale Master and its summons (yes and other defensive buffs). However, it doesn't make sense intuitively that an ESF Necromancer with no Pale Master can summon a stronger Vampire than an ESF Necromancer with Pale Master.