I'm asking similar questions and have some of the same reasoning.
Sony's EReader looks great, I had a quick go with one in the Sony Shop today, but the great investment is always going to be in the books and I don't want to be tied.
I have no legacy ebooks - so the Cybook looks good as a low risk/low regret choice. But my inner geek would love to play with the iLiad.
From a work point of view its would have to be the iRex Reader for decent A4 pdf support or wait to see what plastic logic come up with. But that probably means waiting a year, and that's a long time...
I guess they key is really content. The ability to view it now, and on future devices. After all in the end this is where most of my money will be spent.
Sorry no answers, only questions.