Thanks for the quick responses - this definitely helped me sort out my options! It looks like the flights through CLT are all A321s, plus there is the added benefit of no PHL. While the earlier flight now has 1 more F seat on the seat map, 6 of the 8 exit row seats in rows 9 and 10 are taken. On the two afternoon flights, only 1 of 8 is taken, so it looks like the afternoon is definitely my best bet.