I can only comment from limited experience but we have stayed at both the Majestic and the Rex (2 pools) which both have pools - albeit small and certainly not "resort style" like those one might experience in Thailand or Bali. Then again, Saigon is not a resort kind of town - it's many endearing features lie elsewhere.
Nevertheless, we certainly enjoyed both and I would put the Rex slightly ahead. You did mention that price was not an issue and these hotels are certainly at the more expensive end of accommodation in Saigon. I understand that not staying in PNL and paying more than A$50 a night for a room can make one something of a pariah on these boards, but for what it's worth, we felt both hotels offered genuine value.