Ramp Room
Best place is usually just above half way down the farthest ramp in the shadows with an engineer sitting opposite the two lower entrances, and dispenser half way down the first ramp.
Outside Upper Respawn
Opposite the exit from the respawn room, facing towards the exit from the spiral and ramp room, with an engineer buzzin' around checking all the entrances. Dispenser just down the spiral for spy detection and killing.
Spiral
Half way down in the shadows - if they know you're there, they'll drop grenades around the corner, but if not the suckers will charge down and BOOM. Dispenser a bit further down from it, to slow down those nippy scouts.
Flag Room
Hmm this map is a bitch for good flag defence with one engineer - usually I shove it diagonally at the corner of the FIRST corridor, with the dispenser at the flag side of the SECOND corridor.
