I find Penthouse to be more engaging than Sky Castle because of the plot twists but it was apparent to me from the first episode that the former had more worse writing and acting than the latter. Way too much yelling as well.
They yell too much and get involved in a lot of petty drama. That's one downside of both dramas.
Sky Castle is limited in different ways, obviously, it had a lower budget compared to the Penthouse.