Which Edition?

I am in need of assistance. I recently purchased a facsimile of Shakespeare's first folio. Upon comparing the text of the first folio of Hamlet to the text of another text of Hamlet, prepared by Arthur Henry Bullen, I am noticing a dramatic difference between the two.I am curious if anyone could tell me what sources Arthur Henry Bullen used to prepare his text, and why he deviated from the first folio so dramatically, in my opinion. Thank you.

There should be textual notes in the Bullen edition that show where it came from. If you see any notes refer to (Q1) or (Q2) or (F) they mean, quarto 1, quarto 2, and folio respectively. I am not familiar with the Bullen edition, but it is possible he drew from Q2 a fair bit.

thanks for the information, I am curious, why do editors use quartos, when creating new editions? Why not just use the first folio?

Various reasons. Some prefer the quartos, others believe they are more authentic as they were written during Shakespeare's time, unlike the folio. But the folio is still the most common and most preferred.

The only thing I've really ever heard is the fact that they contain enormous amounts of errors, as they were written from memories of actors and audiences, etc.,as these quartos may have been unauthorized.

Yes, there were unauthorized quartos, and bad quartos - but here you are getting to the authorship mire, which is a difficult struggle.