The best necromancer requires a lot dubious build options, but here it goes:
Use the old Juju Oracle and take it to 4th level. Take a 1-level dip in Sorcerer (any bloodline) and then use a SLA to qualify for mystic theurge. Take the Experimental Spellcaster feat from the optional Words of Power system to learn the Undeath word, then take it again to learn the word with your other class. Due to the precise wording of the Undeath Word, it doesn't actually work like animate dead but instead gives you a separate pool of undead altogether. This means you get four pools of undead minions: 6 HD/caster level arcane animate dead, 6 HD/caster level divine animate dead, 4 HD/caster level arcane undeath word, and 4 HD/caster level divine undeath word. That's a total of 20 HD of undead per caster level. With the magical knack trait, your caster level is only 1 behind your character level in both classes.
So by the 11th level you'll have Oracle 4 / Sorcerer 1 / Theurge 6. This gives you 200 HD of undead.
What Spell-Like Abilities would you recommend for the character. I am not sure what to select. A small list would probably be best if possible.
Also, thank you all for the amazing advice. In a platonic way, I love you all.