PS in parents isn't as important as show levels in parents are. When you breed two horses each PS stat gets cut into a 1/4. Ideally you want to get your horses show levels to be about 50 with your first generations so that your foals with have a training boost (TB) of around 10. This training boost in return is going to boost your PS for every training you do and get you those higher PS numbers.  So that's why you want to go for the levels.

Personally when I'm starting with a foundation line, I put them into whatever is going to give them the most points for show levels. Often times this is halter, but you loose money in halter so that's why it's not often recommended for new ones. So it might take some experimenting. Sometimes I'll enter a day of discipline, a day with halter, and a day with careers and then I compare to see what's giving them the most points. Also remember with discipline you should double what they're earning per show to get an idea of what halter/career is giving them because halter/career take 20% energy and shows take 10% energy. 

So for example if your horse is getting roughly 500 points per show in disciplines and 900 in halter shows, discipline is going to be better because they can enter more shows than halter. 

Then once they reach level 50 I breed them right away until I get 2-3 foals from them. Then I scrap the parents and just work with the foals. 

Thank you! That's really helpful! Also I'm glad to know that halter showing is still going to be beneficial with the parents. In Eqc it was pretty much pointless, if I remember correctly- it just won money and that was about it (I think? That was YEARS ago).