In a criminal case, who present the case first, the government or the defendant, and why?

The government presents its case first against the defendant because the government has the burden of proof. Afterwards the defense presents its case and the government gets to do rebuttal if they wish. In my experience I'd rather have the last word than the presumption of innocence but that's not how the system works.

I am assuming that you are asking who presents the case first in trial. The prosecution (government) presents their case first, because they have the burden to prove beyond a reasonable doubt that a person is guilty of a crime.

That is also why the government attorney's seat is always closer to the jury than the defendant's attorney. The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.