I'd rank them top 10 for sure...most would rank them top 5, but those people like pitching prospects which the Pirates have plenty of. Outside of the obvious two (Taillon and Glasnow) I really like the unflashy Kingham who projects to be a mid-rotation innings eater type. They also have a guy by the name of Adrian Sampson who just got called up to AAA. Again they aren't flashy numbers but turns out he never threw a changeup until this year (or at least never learned to throw one properly)...and it joins his curve as a plus pitch. He looked average solid in the game against Louisville this week. He's gone 6 innings 21 times this year...I love those guys. Pittsburgh is following the Marlins with pitchers that have unsexy stat lines but are effective.
As for hitters, the guy to truly look out for the Pirates is Harold Ramirez, most upside of any prospect in all of baseball. He's lacking one tool which is expected to develop (power). I'm calling it now...if he recovers from the shin injury (and doesn't develop any other injuries). He's top 20 mid-season prospect next year. Maybe top 10.