Upload & Sell: Off
...I am likely to buy at least 1 580EX II and possibly a second if not definitely a 430EX II. My question is about the most effective off camera trigger solution. I could buy the Canon ST-E2, but I see most dont use it and I wonder why?
The ST-E2 is outdated. It doesn't swivel and it's lower in power than a 580EX, so unless one is in a small room where the IR signals can bounce, the slaves have to be forward of the camera -- not always desired.
Also, the ST-E2 is limited to two groups, A & B, whereas Canon's ETTL-II system can handle three groups, A+B+C or A:B +C.
If you have a 580EX II, you can use it as a Master -- either on camera, or off camera using a long ETTL cord -- and use it either as a key light or a fill light, or disable it from firing for exposure while still firing the metering and command pulses. In Master mode, the 580EX/EX II can control three groups, and if using only one slave the flash head can be pointed directly at it for greater range.
As far as radio triggers, it depends on if you're willing to fire the slaves in manual-power mode. If you are, there are many options in a wide range of price points. If you need to have ETTL metering, the options are more limited and more expensive.