Hi there!
While I understand why you’d rather have a species your neighbours don’t have, I think you should not use that argument when buying animals like Parosphromenus. The main point of this project is keeping and breeding the fish not because of their rarity in the hobby, but because of their rarity in their natural habitat. These are highly threatened fish, which should be kept mainly for conservation.
If your goal is having something special rather than saving the species, I’d recommend choosing a more common species, like P. linkei or ornaticauda. I don’t know about the trade in your area, but in the Netherlands bintan and ornaticauda are traded regularly, while linkei and nagyi are common among specialists. I believe opallios is very rare, I don’t think you’ll be able to get them.
I think you won’t really get the chance to choose, since paros aren’t traded frequently. If you do get the chance to choose, and if you’re planning to also breed the fish, I’d recommend taking the most rare species, but even better would be getting both.