Well if the PDFs are mostly text, I think the Kindle fits your requirements (yes, I'm prejudiced).
* Easy to use (total dealbreaker if it's not easy to use)
The Kindle is very easy to use
* e-ink display (doesn't have to be color, but dealbreaker if it isn't e-ink)
No e-ink readers available to the public are color.
* PDF support (isn't an absolute dealbreaker requirement, but it'd be nice nevertheless to have true PDF support without some sort of stupid workaround if absolutely necessary)
For text PDFs, amazon will do the work of converting them for you and send them directly to your Kindle via Whispernet. The turnaround for conversion is very fast. Usually minutes and once in a blue moon an hour or more (if it's wireless network problem).
* Ability to sync with Macintosh (in the case of Kindle, what if I'm in a wireless dead zone? If I can't sync with a Mac, it's a dealbreaker for me)
Use
this link to check availability or strength of Whispernet in your area. I've had my Kindle wireless work in areas where my cell phone didn't... go figure. You can still download to your computer and transfer books via USB cable.
* Ability to purchase eBooks and be able to read them within a few hours (left intentionally broad for a reason)
You can start reading within minutes of purchasing Amazon books on the Kindle.
You can also try the Kindle for 30 days and return it for a refund if it doesn't work for you.