Simple answer
If I had to sum this up in a sentence :
Go for the HV 20, apart from cost it has
no disadvantages compared to the JVC and Panasonic
I had posted a fully reply but a power cut just .. happened and I lost it all ( Im at work ..the end of a second 13 hr Night shift!

Il try again.. shorter this time
Longer version
Very simply put, the HV 20 is your best bet being arguably the best HDV ( and SD) camcorder at that price point. The HC7 Sony is close
The JVC doesnt stand up against it and its big Zoom is down to a smaller sensor which has its own disadvantages
The Panasonic is a good camorder but apart from not being able to capture HDV, it isnt actually a better SD camcorder than the HV20
Futhermore,there are a no of extra features the HV20 has which it doesnt
And
HDV on an HDTV is better seen than described
As such
You can use the HV20 as HDV and capture as SD DV by downconverting in camera "on the fly"
or Capture as HDV and convert in software or output in either SD, HD or both..for playback or archive back to tape
Certainly you can use it in SD mode all the way if you wish should you need to ( say to shoot for someone who doesnt have an HDV camcorder)
What reviews online do you read of the difficulty with editing HD?
HDV editing software is 2 or 3 generations old and the hardware required is pretty much mainstream unless you want to do it with an 8 year old PC running windows 98

I would imagine many of the difficulties you hear about Hi def editing refer to AVCHD. I imagine they well get better as time goes on . HDV a few years ago was harder to edit on hardware at the time. Also clever software has been written to optimise current hardware
The
How do we playback as Hi def ? questionon is common to all Hi def formats but at least with HDV you can always run the tape via the camcorder directly for playbcak even if it has been edited
Dont allow that to discourage you from getting the H20 as it will soon get imposible to buy SD TV and you would be pleased you have todays footage as high Def. The issue of domestic playback formats will get easier as time goes on
Ass such there is no
hassle in getting one now.
With AVCHD it is a bit trickier ATM but its only a matter of time before that gets easier too.
It ( as a HDD ) format has its own archive related questions, needs powerful Hardware ect . but if you wanted to get even an HDD model I would still encorage any of the current Hi def models despite the "hassle"