Help deciding the BBEG for a oneshot

[Kassan]

Hey, so I'm making a oneshot adventure for some of my players to run. They're going to be about 4-5 PCs, starting at level 5. But I'm having trouble deciding which adventure to run, as I've made three. Basically, it comes down to the BBEG of the adventure. We try to get a healthy mixture of RP and combat, about 50/50. What are your thoughts on these three scenarios?

1) False Hydra. Paranoia incarnate.

2) Cultists and Undead. A classic, though I may spice things up by making all the undead slightly intelligent.

3) Slaadi. May be a bit tough for level 5's, but I'm not planning on throwing mobs of Greys at them.

[JNAProductions]

¿Por que no los tres?

A chaos-infused undead hydra, worshipped by a cult. Each time a limb is removed, including a head, 1d6 random new limbs grow out of it of many different types.

[HandofBlades]

Mindflayer priest controlling the town through the mayor and sherif. Wips up a mob against the pcs when they invade the crypt beneath the church and discover a small portal to the far realm.

[sir_argo]

Cultists and Undead. A classic, though I may spice things up by making all the undead slightly intelligent.

Y'know, I've always wanted to run a scenario where a cult is converting captured villagers into zombies. The characters have the moral dilemma that every zombie they kill is an innocent person that can no longer be reverted back to a normal person. I picture the ritual to include tattooing a rune to the villager's forehead and the party has to figure out how to safely erase it to save them.