Hey
a330300-dude,
Seems like you'll be arriving in DC right when people are rushing home. Definitely take the IAD option that arrives later in the day. Who knows, your Mom would give you plenty of brownie points for not having to deal with traffic that's ten times worse than do the Bay Area.
Maybe you won't have to clean your room for a month! Maybe she'll buy you ice cream! Or an In N' Out Douba Douba!

(sorry, it's lunch time here)
Jamester