Or combine the two and take Undead Leadership.
How about C) All of the Above?
Leadership + Undead Leadership + Animate Dead + Rebuke/Command + Command Undead = "Me and what army? Why the one right behind me!"
Forgot Draconic Leadership or whatever gave you a dragon cohort.
Also Wild Cohort.
I want to make this character so bad now...
Dread Necromancer if you want to specialize in Undead armies, with Leadership, Undead Leadership, Draconic Cohort, and Wild Cohort (if I could find the book to make sure it works). Throw in Extra Followers. If you could get it house ruled that you can take Prestige Classes and keep boosting Undead Mastery then maybe something like Malconvoker. OR be an (Half-)Orc and take Orc Warlord 3 + Extra Followers
So (Half-)Orc Dread Necromancer 17/Orc Warlord 3 with Leadership, Undead Leadership, Draconic Cohort, Wild Cohort, and Extra Followers. Then have your Cohorts take the same feats, -Wild Cohort for the Undead and -Undead for the Living. Make them DN and the living DN/OW. Just to make it easy, assume they have a +10 Cha Mod.
DN: 17*14 + 17*14 + 14*14 = 672 HD
Follower Multipliers: *2 for two leaderships, *2 for OW, *2 for Extra Followers. Then *2 for two leaderships, *2 for Extra Followers and *2 for OW and *2 for Extra Followers. I'll also assume Max Leadership for the Cohorts (since they can mooch off your maxing the score and +10 Cha Mod = >25) So we have *6 at max on the table.
Base Followers: 135, 13, 7, 4, 2, 2. Multiplied = 810, 78, 24, 12, and 12.
Add it all up: 1608.
In addition, you have 12 guys who can take Leadership, with 5 (2 from main, 2 from living, 1 from undead) taking Orc Warlord 1 for *1.5. Say their Cha Mod is 5, so their leadership score is 11. That's 6 followers, 9 from the OW. 45+42 more.
Overall you should have 1695 followers. (But I probably butchered the math somewhere and/or it's unoptimized)