04-21-2014 11:19 AM
The 430exII is a more powerful flash with additional features, so it could be called the “better” flash. Either flash will work with any of Canon’s digital SLRs including the 70D.
But no, to answer your second question, you can’t use them for movies. All Canon flashes are strobes, they provide a temporary burst of light for still photography. For movies you need continuous lighting.
04-21-2014 11:55 PM
The Canon 320EX does have an additional continuous LED light for video, but the reviews I have read said it is not very bright and of limited use.
04-22-2014 07:53 PM
04-22-2014 08:12 PM
04-23-2014 10:32 AM
I had a 320 and the continuous LED light was horrible. Any movies you'd shoot would feature friends and family cursing and shielding their eyes in a horrible harsh spotlight. Kind of like the creatures in that Vin Diesel movie Pitch Black.