I always book my own flights because.
a) I live in Houston and I can get direct flights pretty much anywhere in the US.
b) I have elite status on Continental.
c) see b and chose my own seats. (no middle seats)
d) see b and no checked bag fee
e) see b and shorter security lines at the bigger airports
f) see b and early boarding (over head bin space)
g) see b and good chance for a free upgrade to the big comfy seats in the front of the plane
f) I can decide which flight and or airport works best for me.