For an updated comparison featuring the newer Canon flashes, including the 320EX and 600EX RT, visit my Steele Training website and watch the free video there. I tried to post it here but for some mysterious reason it was rejected.
You can also find other photo gear videos on my site which are not here on YT.
I was hard on the little 270EX in the video, but it's actually a great flash if you are using a compact camera with a hot-shoe, like the G10. Otherwise, for DSLR cameras, I recommend the full-size flashes.
If you buy from my Amazon links you put a few dollars in my pocket and help me produce these tutorials.