In principle it's FF, but in current practice would be HP due to gerrymandering. Congress could mandate a neutral commission for CDs to eliminate that weakness. Then candidates would be seeking swing districts to compete in, not just swing states.
If POTUS were elected by CD, then the Dems would have a much stronger case, that the CD lines need to be gerrymandered in their favor, to offset the GOP's geographic advantage, given the concentration of Dems in large inner cities. If it takes say a Dem getting 53% of the popular vote, with CD lines drawn per the Muon2 metrics, in order to win a majority of the CD's (that is probably an estimate this is not very far off the mark is it?), then the system is a fail out of box.