Best way to western Suburbs of Philly -
Agreed on the 'avoid DC-Baltimore' thought, although with the opening of the new high-speed lanes, this leg of I-95 is not as bad as it used to be, and in times of good weather and no detrimental traffic conditions, it's actually quite easy to get from DC to Wilmington DE.
That said, there are two possible alternatives that will provide a more relaxed ride, although a longer one, time-wise.
1) CBBT from Norfolk to Cape Charles, then north on US 13/US 113, to Dover then North on DE 1 to I-95, then North on I-95 through Delaware and then I-476, the "Blue Route", from Chester PA to the Bryn Mawr area, which is probably the US 30/Villanova exit. I-476 can get congested and slow if there's any kind of a fender-bender, as PA drivers love to slow down and see if there's any blood on the pavement. Gaper Blocks were invented there.
2) US 301 from anywhere south of Richmond, north through the Fort A P Hill area, across the Potomac, and then join with US 50 east of Baltimore, east across the Annapolis Bay Bridge, and then north again when US 50 splits off towards Ocean City MD. US 301 up through the Eastern Shore and Delmarva is a flat, easy, simple ride with no traffic lights or other delays from just north of Queenstown until you hit Middletown, DE. Once in Delaware, just follow the signs for I-95 north, and follow above directions for I-95 and I-476.
You could also take I-495 up along the Delaware River to Chester PA from south of Wilmington, it cuts out some of the slight congestion in Wilmington.
Not sure when you're planning this trip, but in nasty weather I'd probably do the US 301 route, only because the Annapolis bridge isn't quite so tricky in bad weather compared to the CBBT, and the rest of the way is high and dry.
Here are tracings of the US 301 route, the US 13/113 route, and the area between Wilmington, DE and Philly. Hope this helps.
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