The big difference I would like to point out here is the codec. The xf100 uses an mpeg codec with a 4:2:2 color space as opposed to the 4:2:0 color space of the XA20.
The XA100 footage will give you a lot more leeway in post production. Granted, you'll need an editing program and computer that can handle the 50 mbs stream. You may be surprised what a little grading in post can do for otherwise dark and muddy video.
There was a day when I was all aboard the AVCHD bandwagon… but now that I've radically upgraded my edit station and software, I yearn for a better codec than my current cameras provide.
I should also mention it may have been all the ACVHD processing that totalled my laptop… so… word to the wise – airflow. AVCHD takes a goodly amount of processor power due to it's highly compressed nature. High processor use equals heat.
Here's what Philip Bloom had to say about the XF100 and the XA10…
http://philipbloom.net/2011/07/09/video-review-of-the-canon-xa-10-xf100-and-xf105/
For things to consider not related to image quality:
XA20 has most functions buried in menus. XF100 has more external controls. Verdict – XA100 is easier to use.
XF100 looks more impressive to a client than the XA20. I know, this is lame, but it's a fact of life when people who know nothing about cameras are paying you. Verdict – XF100 will get you more business.
XA20 has 1080 at 60p. XF100 has 60p at 720. Verdict – Slight edge to the XA20 in slow motion IF you're viewing in a theater or on a particularly large TV. Either way, slo-mo needs several times as much light as 24p to make it look the consistent with the rest of your footage.
XA20 has a 20x zoom vs the XF100's 10x zoom. Verdict – XA20 -especially for event video.
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