Pocketwizard Mini/Flex or PocketWizard PLUS II Transceiver
 

I am looking to buy some of these and was wondering which ones was the better

I have a couple of canon speedlite 580 and an old 420EX and am looking to

fire one through a Lastolite softbox, one through an umbrella kit

and one for the background.

As I havent got the umbrella kit I was also wondering whether to buy another

softbox kit or whether to buy the Lastolite umbrella kit

can anyone give me some advice which would be better

I don't know whether you sorted this out yet. I've got both the Pocketwizard IIs and the Flex/mini.

The Flex/mini have more functionality, for instance they can use TTL metering remotely which the IIs can't. The mini is smaller than the II. They can do everything the IIs can do & a bit more

The pricing isn't too different so you might want to go with the Flex system for future proofing, though if you don't think you'll use off camera ETTL remotely & you can get a good price on IIs you won;t be disappointed, they are a great bit of kit.