I live in the Philly suburbs, our highways are all a bit of a clusterfuck but if I had to choose

I476 (Northeast Extension to the PA turnpike) between about midcounty and Lansdale, maybe Quakertown isn't usually too bad traffic wise, above that is probably the prettier drive but there is always some mind-breakingly bad traffic and/or construction whenever I go that way.

I76 (Schuylkill Expressway) between the city and Conshohocken is kind of nice if you're on it at like 3AM when there's no traffic, some really nice views of Manayunk and Boathouse Row and such, most of the rest of the time it's a parking lot.

I76 (PA Turnpike) is usually pretty nice further out west when you're away from major cities

It's an absolute madhouse of different lanes and is always busy, but the NJ turnpike somehow manages to keep traffic moving better than nearly any other highway I've ever driven on.

A lot of the smaller highways further up in the mountains (usually) don't have too much traffic and are very scenic, but you have to be at least an hour and probably 2 or 3 out of Philly to get the most of that, and at that point I often can't recommend getting off the highway to interact with the locals.