I can't speak to HIPness, I'm afraid. Haydn drew me to the form and I went looking for anything in a SQ that promised to be "what he said", like his. I was disappointed, intrigued and challenged by how hard it is to find 18c SQs, thought there'd be scads of them, but there aren't.
My ear channels them into 2 broad categories:
1. Wiener, sophisticated and ambitious, given to a certain edginess - whoever isn't in category 2.
2. Francais, decorative, satisfied to be pretty - Haydn prior to opus 9, Gossec, Gretry, Zimmerman, Rigel, Boccherini (as a rule), Boulogne, Lombardini, Rosetti, Hoffmeister. (And I refuse to denigrate these - nothing wrong with pretty.)
No grand claims here, these are my impressions.
The Titz set on Profil is outstanding, and HIP I believe. Other standouts are Eybler on Analekta and Wolfl on Caro Mitis.