Both: PA gets to tax the K-1 because the income source (rental) is there, and DE gets to tax it because you live there (your resident state gets to tax all of your income regardless of source).
Prepare the nonresident TT/PA return first, then your TT/DE resident return so that TT/DE can prepare for you the other state tax credit for some or all of the PA tax on the rental income that DE is also taxing - this helps to prevent double taxation.
