I just have to comment. I swear I have NOT found the "perfect" system yet. Each one comes so close ... and then misses it.
I jumped on the RadioPopper bandwagon when they first came out. I used the PW TT5 system for several years. And about 6 months ago switched to the Canon 600s with with the ST-E3 remote.
My very most favorite thing about the PW was the AC3 Zone controller. With REAL/PHYSICAL switches and dials I could adjust settings without even looking at it. A bride could be walking down the aisle and I would have one set of lights flashing, then as she passed me I could switch to a different set of lights by quickly turning one switch off and another on. I barely had to take the camera away from my face long enough to flip the switches and then resume.
The downside to TT5 is the stupid RF interference with the Canon 580EXII flashes. I had 5 of those, all with socks on them and still had issues of flashes sometimes being too far to fire reliably (at just 20-30 feet!).
I love the reliability of the Canon 600s. I love that I have 5 groups to play with. I love that it works essentially the same way as the AC3 Zone Controller (being able to turn individual lights on or off, ettl or manual, etc).
What I _hate_ is that there are far too many button presses and dial turns to accomplish a single task.
Turn a light off:
AC3: flip a switch (often without even looking)
ST-E3: put remote down below me where I can see it (old eyes aren't helping), push a button, rotate dial to appropriate group, toggle off
Change the power setting is the same:
AC3: return a dial (often without even looking)
ST-E3: put remote down below me where I can see it, push a button, rotate dial to appropriate group, push a button, rotate dial to desired power level
Too many button presses and dial turns - all of which require that I watch the screen while I'm doing it because all of the buttons are "context sensitive" (meaning they change what they do based on what is on screen at the time).
I would PAY EXTRA MONEY to get a remote that let me control my lights with physical buttons and dials like the AC3 Zone Controller.
Please pass the word along to Canon.
Try out the Yongnuo YN622C then. I have 5 transceivers and after putting complete faith in them for a number of jobs they've never let me down. I haven't tested beyond 30m but have mixed and matched the flashes between the 550Ex, 580EX, 580EXII and 600EX with no change. They have physical buttons, Hotshoe passthrough, AF assist beam, batteries last a lonng time, they are reliable, HSS is not problem, can be controlled entirely in camera if you want, etc etc. You could put the flashes down the aisle and press the group button by touch to change the channel as the bride moves. These things are absolutely fantastic. You can customise lots of functions too like remote flash zoom, mixing of ETTL and manual metering, PC Sync port built in and link lights blink on metering start. The RT system is amazing but very expensive and still limited more than the YN622C. I thoroughly recommended anyone doing remote ETTL to research and buys these....you won't look regret it!