I would go for the Sony. neither Onyx nor Goodreader come close, Onyx is heavy with no touch screen, Goodreader software doesn't look good (check videos, see the response time when writing notes on PDF)
$600 is better deal than both can provide, and you get better hardware and software quality, if you need professional PDF reader and note taking.
I still have high hopes that Sony release some update in the future. no information, just hopes