I have a one year old HV20 and a 2 month old HF100. First and foremost, I care about video quality, but convenience is also important.
Each year, we go to the Fraser Valley in Colorado - an area surrounded by pine-forest covered peaks. Last year, we took a ton of footage with the HV20. Did the same this year with the HF-100. Three fundamental things about the video quality strike me in comparing similair footage.
1 - the HV20, given any movement at all, still has a slightly better ability to resolve fine detail. In bright indoor shots and in in reasonably but not overly detailed outdoor shots, not sure I can tell the difference. However, the moment I have a backdrop with lots of pine trees on distant hills, there is a very noticable difference. The HV20 simply seems to resolve a lot more of the distant pine detail. The HV20 did (and does) create a "wow" factor with those kind of shots. The HF100 does not. The 100 is not bad, but I lose the ability to marvel at the distant detail. Of course, thousands of pines mean millions of needles. That's a lot of detail. And my camera is never completely still in real life - even if only slowly zooming or panning (or if there is some movement in the subject/s). This is not a small quality difference. (I should note I have a 65" 1080p projector - smaller screens may not reveal such a big difference).
2 - Movement is more fluid with the HV20. With the HF100, I noticed that I found even reasonably slow pans bothersome - there was blur and greater "blockiness" to the scenery. The HV20, on the other hand, seems both more fluid and to present more of a solid image as I pan - really allowing my eyes to track the scenery during a pan.
3 - Medium to low light shots are dramatically better on the HF100. With the HV20, I tried to do all kinds of things to compensate any time it was evening in doors (even with a few hundred lux of light) or nearing twilight outdoors. The colors seemed overly reddish on the full auto settings, the image got noisy, etc. I used cineamode to try and offset both to some reasonable effect. By comparison, I have found I never need to take the HF100 out of the "Easy mode" and the quality is far better than what I got with all my fiddling on the HV20. (I should note I do all my filming in 60i - so bear that in mind). This is no small quality difference. It's huge.
In the end, for video quality, I'm faced with having to let go of the occasional "wow" factor in higly detailed (and real world - with movement) shots for the much greater quality consistancy under varying lighting conditions. That's not an easy trade-off, but probably tips the scales for me to the HF-100.
If you are a hobbyist or such who can always assure ample lighting - the HV20 probably still reigns for best quality.
EDITING AND CONVENIENCE - another matter entirely. If you want to do a lot of post work, there's still no comparing the tools available. I do not do a lot of post work. I was pleasantly suprised by the packaged (Pixela) software. It's not great, but for scene deletions, trims and rearrangements, it works while doing smart-rendering, which is a big deal for time and quality. So that suggests the HF100 for me.
For distribution, the jury is still out, but it looks like AVCHD will win out. There is some suggestion that Hi-Rez MPEG2 (HDV) can be natively encoded to Blu-Ray disks. I haven't tried that. But I can say that that the AVCHD disks created on DVD from the HF100 play very well on the Play station 3 and several other Blu-ray players I've tried them on. All my connections are via HDMI - and there is no perceptible quality loss to me vs. hooking up the camcorder straight. That's promising.
I took my Colorado HV20 footage and encoded to AVCHD (17Mb/s). I used Pinnacle Studio 11 - probably not the best encoder. But the important point is that, even though TWICE compressed with the re-encoding, the resulting footage was, in general, better than the AVCHD from the HF-100 for the highly detailed nature scenes described in point 1. That's really surprising and is good news for the standard. It suggests any quality trade-offs I'm seeing today may be more a function of processor limitations (doing it all in real time) vs. the protocol(s).
I'm still struggling, but in the end, I think the more consistant quality with low light and the distribution convenience probably will make me shift to the HF-100 and AVCHD.
For what it's worth.