I haven't ridden either, since I didn't have a bike when I lived in Erie. The PennDOT route doesn't give me the screaming mimis in Erie proper, and it *seems* to be staying on sensible roads. Please note I'm *not* an Erie native, so I'm going on memories of college from a couple years back. The Adventure Cycling route is less clear in the online version so I don't know what I think (beyond the obvious bit of why are they hauling people *that* far out along the lakefront if they're not gonna let you bike in the park - Presque Isle is gorgeous and I'd almost class it as a sin to be in Erie and not wander around there).
The routes are different because PennDOT and Adventure Cycling aren't the same group
. They have different priorities. Both seem to be routing you along PA state highways. These are typically 2-4 lane roads with unrestricted grades and 1950s lane widths. Usually no shoulders. They tend to be less traveled, since they're not well marked. If you *do* hit a US route, it should be similar.
Silly question: do you live in PA or will this be an Exotic Vacation for you?