PAM184 - 42mm steel Radiomir GMT
PAM242 - 45mm steel Radiomir GMT
PAM244 - 40mm steel Luminor GMT
So what you need to decide 1st is which Panerai case you want - Radiomir or Luminor? Pick the Radiomir if you want a more dressy watch and the Luminor if you want a sporty watch.
After that, then you need to decide on how large the watch you want. The Luminor GMT also comes in a larger 44mm case such as the PAM88.
Cheers,
Anthony