Naw, you can use the HDMI cable with the iPad1, as long as you are running iOS 4.3.x.
I can't answer the question about clarity (cause I only have the HDMI cable - got nothing to compare). But, wouldn't it sound logical to say that HDMI would be more clear than av cable ... as a general rule?
That's a guess, but maybe some other "cable" person would know that answer...
Marilyn