| Missle Turrets. I haven't taken a look at how much damage the spore colonies do (I'm sure that the Photon Cannons probably do the least damage against air, since they can attack ground as well), but the Missle Turrets have a trump card: they can be repaired.
And I guess it depends on what kind of map you're playing on. For a money map, spore colonies would probably be better, but on a Blizzard map, where resources can be scarce, repair is a very handy feature that I use frequently now.
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