I tend to be biased. I made a careful study of the pros and cons of both AVCHD and HDV cameras before actually buying one, and settled on the HDV model (Canon HV20) because I was very familiar with mini DV tapes and because there were no particularly special requirements for editing the format. Essentially a decent computer and VS10+ would do a good job.
AVCHD, on the other hand, presents advantages in terms of the size of some of the cameras (the ones that use USB storage tend to be very small) and the quality of the video for the size of the files. But it seemed -- and still does -- to be a format which has not yet quite settled down. The different camera manufacturers appear to trying out new standards and AVCHD codecs. And as usual, the software manufacturers are scrambling to catch up. They haven't managed to do so convincingly as yet. And this is not to mention the fact that you require at least a decent Core 2 Duo or Quad to have a chance of not only editing your AVCHD, but even playing it back smoothly on the computer.
Usually, the AVCHD cameras come with some basic proprietary editing software made by the camera manufactuer which works with that camera. But it is indeed basic. The bottom line is that, in my opinion, AVCHD cameras are still better for those who want to point and shoot, not do much editing and quickly play things back on a HDTV. More serious users still face enormous editing hurdles, and no one yet seems to have brought out a perfect program within the budget of most average users.
As for quality, to me they are much the same, though AVCHD quality can vary considerably because there are so many varieties of it, depending on the camera -- both in terms of the codec/technology, and the frame size, bitrate and other properties used. So when I say the quality of AVCHD and HDV are pretty much the same, I am talking about AVCHD shot and edited using high quality settings (1920 x 1080 and a bitrate of around 18 Mbps -- though Canon now has an AVCHD camera which uses a bitrate of max. 24 Mbps. But that is one that VS and other software packages have severe difficulty with.)
Although there are a couple of variants of HDV, essentially another advantage for me is that there is a main single standard (1440 x 1080 at CBR 25 Mbps). And that is easily as good as top quality AVCHD. Some even argue that it is better, though perhaps my eyes aren't up to the job of detecting any significant differences. (I can, however, easily detect AVCHD which has been shot using lesser quality settings when compared to HDV.) One argument is that AVCHD tends to show high definition shimmer in fast panning shots more than HDV, and this may be so, but fast pans in HDV are also pretty awful and best avoided.
The downside with HDV for many users is the same as its main upside for me -- the DV tape. As with SD mini DV cameras, everything is done in real time. So one hour of HDV video takes one hour to capture. With an AVCHD camera, transfer of the video to computer is only a matter of seconds. Fortunately, I am patient!
As a final comment, there are quite a lot of predictions that mini DV/HDV is probably on its way out at the consumer level. But the same predictions note that it will remain the preference for professionals. For me, that says a lot in support of the strength of the HDV format and I am more than content to stick with it for the momet.
Oh, and as for your other question: yes, you can send the edited HDV back in transport stream format (like it is shot in) to the camera, and then hook up the camera via its HDMI port direct to the HDTV. The camera then in effect acts like a mini Blu-Ray player... A warning here, though: VS11.5+ and 12 both seem to have a problem doing this with Canon HDV cameras (but not the other brands). This problem was first noticed with VS10+ and Ulead, as it then was, brought out a patch which fixed the problem. But for some unknown reason, this was not included in the later versions. (Adobe Premiere Pro CS3 also has a similar problem with Canon HDV cameras. I don't know if this has been fixed with the recent CS4.) Anyway, I am lucky that I still have VS10+, and so I have used that to successfully send my edited HDV back to the camera.
Now, however, I have to admit that I don't bother since I have bought a PlayStation 3 which I have networked to my computer. I can thus stream my edited HDV from computer to my HDTV via the PS3. The result is simply marvellous. The PS3 will also play HDV (and AVCHD) copied to either a USB stick or external USB hard drive (formatted in FAT32), and also play edited HDV burnt as an archive on an SD DVD. It will also play 'hybrid discs' which are high definition AVCHD burned to a Blu-Ray format directory on a standard definition DVD. So all in all the PS3 is a versatile device which opens up the whole world of home high definition video without the necessity of having to move immediately to expensive Blu-Ray!
