I bought both and returned one.
- Epson has more pronounced screendoor effect. If you don't like that, Panny's better.
- Epson was a lot louder. If you're sitting near the projector and care about noise, Panny's better.
- Epson had crap lens shift controls, but that doesn't matter after you've set it up.
- Epson (at least the unit I had) had a serious firmware bug with HDMI CEC that basically bricked the projector when HDMI-Link was turned on.
If none of the above are issues for you, I'd call it a toss up, slight edge to Epson for blacks.
As for me, I returned the Epson and kept the Panny. Loving it.
Don't go for a dirt cheap retailer. Use a good one, authorized. 2 out of 3 specimens I received were defective in some way or another and had to be returned.