I've got a Canon 580EX II and use it mainly on my 5D3 but I do have a Nissin Di866 Pro MkII which also gets used as an off camera flash for multiple light shots on the 5D3 as well as being the main flash for my 70D. I don't like the on camera flash look so always have a flash with me. The 580EX II has been superceded by the 600EX RT and it's a bit expensive but very good. The Nissin Di866 Pro MkII is usually around £180-200 new and is probably 90%+ of the 600EX RT but around half the price. The Yongnou flashes are always getting great reviews but I've not tried them. There's usually a few flashes going in the classifieds, usually ranging from the 430EX II upwards and are usually reasonably priced as well.