If both your Macs are made in the last 4 years, i would think they both have gigabit ethernet. I just transferred a few big files between two macs with file sharing turned on and put an ethernet cable between them, it took some fiddling to figure out things, you can also set the finder prefs to show networked places on the desktop which is helpful for me.
Anyway, the gigabit ethernet was very very fast, I was amazed to see a 550 MB file take a few seconds to move over.
Airport is simpler in that you dont need any additional hardware but it is the slowest.
Usb hard drives and flash drives cant be beat for being handy to move files around to any computer, speed is ok, I thought the Gigabit network was faster.
But I have a $20, 4GB flash drive to move files around when i need to and you can take them anywhere in your pocket. I see 8Gb ones now for $30
Firewire target disk mode is good if both have firewire 400, it isnt too hard to set up and the speed is somewhat better than USB 2.0, if both have firewire 800 then the that would be the fastest way to move data by far.