Still birds. Therapoda, sauropodomorpha, and ornithischia all have a common ancestor (and, in fact, that common ancestor is the taxonomic definition of "dinosaur").
So, if you've got the genetic modification mojo sufficient to dial a bird back to something resembling therapoda, you can do the same for its sister classes. Probably using bird eggs, replacing the nuclear DNA, and fertilizing/hatching the result.
Ornithischia would be particularly easy, since the build/gait of that family is explicitly birdlike.
Now, as Shadowzee suggests, you could potentially cheat with sauropodomorpha with some modern animals and extensive modification, but a combination of genetic modification and breeding would probably more closely approximate "dinosaurs".
This all said, to quote Dr. Henry Wu:
Nothing ... is natural, we have always filled gaps in the genome with the DNA of other animals. And if the genetic code was pure, many of them would look quite different. But you didn't ask for reality, you asked for more teeth.