Who was the original choice to play partner on NYPD and Miami Vice?

There seems to be some confusion in your question. You are asking about two separate shows, NYPD Blue and Miami Vice, and you are referencing a "partner" which is a common element in both shows, but these are not the same roles.

* NYPD Blue: The original choice to play Detective Sipowicz's partner, Detective Bobby Simone, was Michael Rapaport, but he was replaced by Jimmy Smits after a few episodes.

* Miami Vice: The original choice to play Detective Sonny Crockett's partner, Detective Ricardo Tubbs, was Steven Bauer, who is the only actor to play the role in the show's run.

It's possible you're thinking of another show entirely or confusing the actors. Could you please clarify what you mean by "partner" and which show you are asking about?