The third (as of this writing) Dracula vs Frankenstein fell to Spain, and cult/exploitation director Jesús Franco.
Shot around the same time as Adamson’s film, this one is also a loose sequel to Franco’s Dracula, Christopher Lee’s non-Hammer excursion as the vampire lord.

Although released before the others, it didn’t receive the title until later in its history.

I have been unable to find this movie, but the scenes I have seen suggest it boasts higher production values than the other Drac/Franks, and a premise closer to Stoker and Shelley.

The clips also suggest it isn’t significantly better, but perhaps I’ll update one day, with a more studied response.

Director: Jesús Franco
Writers: Paul D’Ales, Jesús Franco
Cast
Dennis Price as Doctor Frankenstein
Howard Vernon as Drácula
Paca Gabaldón as María
Alberto Dalbés as Doctor Jonathan Seward
Brandy Brandy as El Hombre Lobo
Fernando Bilbao as El Monstruo de Frankenstein
Britt Nichols as Chica vampira
Geneviève Robert as Amira
Anne Libert as Primera víctima de Drácula
Luis Barboo as Morpho
Josyane Gibert as Estela, la cantante de cabaret
Daniel White as Danny the Innkeeper