In terms of rarity, both the PAM233 and PAM268 are regular production watches so I wouldn't consider one more rare than the other.
Do you currently have any Panerai's? If so, which ones? Radiomirs or Luminors?
If this is going to be your 1st Panerai and your only Panerai for a long time, then I would choose the PAM233 because your 1st Panerai should really be a Luminor IMO. The trademark crown protector is distinctive Panerai
If you already have a Luminor, then I'd definitely get the PAM268 instead.
Cheers,
Anthony