I guess it all depends on what your needs are. If you need higher res and care less about control then HV20 would be great. DVX100's features still make it worthwhile for creating great looking 24p movie, in standard def.
Check out this movie made with DVX100 + 35mm adapter.
http://www.mysimilo.com/
Not saying that you can't make something like this with HV20 + adapter combo, but except for higher res everything else would be a little trickier due to lack of full maunal control. But if you asked me, I would go with HV20, because I know the difference between 'impossible' and 'tricky'.
