Try searching around the forum. There have been 800 million discussions on this subject matter (price, what to buy, this or that). The big thing that stands out for me in difference is 24p.
I saw the DVC30 at the EXpo, it has infared for extremely low light and it does that in BW of course. It was pretty sharp. It is smaller than the DVX 100a, but has 16x optical zoom, I tested the digital zoom, there was no pixelation, it was pretty smooth. Has less manual controls and settings than the 100a. It is a cute little thing.