[Antilochos]

Gasly for me out of those two. Red Bull / Toro Rosso are pretty ruthless with their drivers though. Carlos Sainz is the best driver I have seen come through though that system, I think he's potentially better than Verstappen.

I think Saintz is good, but certainly not that good (otherwise the other top teams would of snatched him away in stead of a complex deal with Renault).
So far, I think Vettel is still their best product, but Verstappen will surpass Vettel as a talent next year for sure (results is a different thing). Then there is Ricciardo who I also believe is better then Saintz, with the latter as a number 4 in that program. But that's my personal view.

1. Vettel / Verstappen
2. Verstappen / Vettel
3. Ricciardo
4. Saintz
5. Kvyat
6. Etc.