Cannibals (aka White Cannibal Queen) is probably one of Franco's worst. Usually, his bad ones are more boring than funny, but this one's hilarious. It's like he'd never even seen a Cannibal movie before and only heard about them.
A Virgin Among The living Dead is my favorite of his, so, I'd recommend that one above all. But you may also like Wicked Warden, Lorna The Exorcist, Female Vampire and Countess Perverse.
As Tromes notes, bad Franco is usually more tedious than funny. I really like Devil Hunter though. Tons of nudity, some ultra cheap gore, ineptitude a-plenty and within it all, an actually rather fun sly dig at "civilised" society.
Vampyros Lesbos is worth seeing just for how damn weird it is, and Faceless is good old-fashioned gory fun. Most of his films that I have seen are a real challenge to sit through.
Lorna, the Exorcist
Female Vampire
Virgin Among the Living Dead
Awful Dr. Orlof
She Killed in Ecstasy
Diabolical Doctor 'Z'
Countess Perverse
Vampyros lesbos
Sinner: The Secret Diary of a Nymphomaniac
Eugenie... The Story of Her Journey into Perversion
A Virgin Among The living Dead is my favorite of his, so, I'd recommend that one above all. But you may also like Wicked Warden, Lorna The Exorcist, Female Vampire and Countess Perverse.