timofonic,
If reading technical documents is what you do most, then the iLiad is your best choice. I know it's considerably more expensive, but all the other readers suffer from the smaller screen which makes it almost impossible to work with complex documents. But if you want to stick to one of the other readers, I can tell from personal experience that cacapee'
pdflrf tool works quite well for converting complex PDF files for the Sony Reader screen.
Right now, the iLiad is by far the most "open" system when it comes to changing the firmware. So if you like messing around with Linux, you may want to consider this.