I have done a side by side with 1080i of the same subject, with both cameras.
The image quality is virtually the same. I also own a 25K Ikegama HD monitor, so you can trust me the images side by side are as close as you need to call them
The differences are the flexibility of the two camera’s. There is no question the Panny is more flexible, for reasons already stated above.
The format, DVCPRO HD is easier to edit, while the Long GOP MPEG2 is more time consumer.
The Panny also has digibeta quality SD recording, with DVCPRO 50. This means your SD recording will be better with the Panny over the Sony.
The work flow is different too. While the Sony has a tape backup and it’s cheap to buy tape, you will have to archive your project clips, that’s going to mean a hard drive, or drives. In other words, count on buying a minimum of 1-2 P2 cards. Plan on buying a P2 Store, or FS100, and plan on some other backup drive. In the short run, the Panasonic will be more expensive, while it will be shorter to get your return on the Z1U
So, those are as I see it. I own both a FX1 and a HVX200. I recently sold the Z1U, but I also have the HDV deck.
Good luck with your choices.
DBK