Hi,
I use 580(11)s & 550s. The 430 is supposed to be good but is slave only in a wireless set-up.
Specifically on the 550, I wrote this here a few months ago:
In general the discontinued Ex550 was a very effective powerful & reliable ETTL unit.
They are still easy to find second-hand & in the UK, mint examples can be found for c £135.
Recycling is not as quick as either 580 unit, although with Hybrid NiMH batteries onboard they are not too slow.
In ETTL they have virtually no limitations – they make very good master units to control 580s, 550s or 430s. The ‘off-master-slave’ switch is much better than the Ex580(11) software switch.
There is one area that I am not sure about; in Canon ‘Manual Wireless’ you may not be (ie. I am not) able to remotely (from the master) vary the output on a slave if the slave is a 550Ex and the master is a 580Ex (either type). Jury is still out on this one. (580s as both slave & master – no problem. 550s as both – no problem.) Just to be clear – this is with ‘M’ appearing on the flash screens. This does not apply ie there is no problem, when ‘ETTL’ shows on the flash screens.> >
Hope that helps.
Donald