It depends what you want.
The 10v is faster, normally, has a better graphics card [shocking] and more standardized hardware.
However, the 1010 can have a HD screen, and ... umm ... yeah, I think that's really the only positive.
I am LOVING my 1010, though, I have to say. It's super-awesome.
In the end, though, they aren't too terribly different. I don't think you'll notice much of a difference unless you try installing Linux.
Received lowest quality mini 9 with 512 megs RAM, 4 GB SSD. Additions:
-2 GB RAM
-4 GB SSD [2 GB SD Card: getting 16 GB SDHC]
Sold for $180 so I could buy Mini 10, XP/Ubuntu, 160GB HD, 1GB RAM, 1366x768 screen, 6-cell for $260.
[Extra screen space IS AMAZING, as is having a working keyboard]