Both are very, very different sounding earphones.
It's really an apples to oranges comparison. You'll prefer one or the other depending on the characteristics you're looking for.
Both are good products in their own ways, each showing that they excel in select areas and doing generally well in most areas. Neither does anything terribly wrong, and both are well priced for their performance.
Personal preference, I feel the PFE is on a whole other level from the RE0, but it's a lot of preference in what I think is important in sound reproduction.
Some of the comments so far are kind of laughable.
I agree the RE0 is well balanced, decently neutral/natural sounding, but slightly dark. I agree the PFE is slightly "fun" in gearing. Bright, eh, not really, although it does present more midrange then some may consider "normal" and has a couple treble peaks that add a little extra to the top end. There is a specific bump in the bass range though and does make tonality a little warmer. With the black filter, it is much more so. Smooth, no. I have not heard another earphone yet that matches the exactness of note of the PFE earphone. There is NOTHING smoothed off about this phone.
I'm partially with ibis99. There is a LOT of hype over this earphone. There is some good reason for it as the RE0 does do certain things really good. I haven't heard another earphone with as much range as the RE0. The frequency response extension is really quite good. Frequency response is also pretty good and even. It offers a clean sound and a good amount of detail. It doesn't do a whole lot wrong. I have personal preferences against it. Sound stage isn't godly and lacks a bit in accurately creating space and location of singers and instruments. It's not the worst I've heard but also not the greatest. It lacks dynamics and sounds very compressed in the sense that every note, every sound made is the effort of a lot of work. It has an energetic, crisp note but without the supporting energy and authority that should be there. It makes the overall presentation sound small and weak even when amped. I think the RE0 needs a LOT of wattage, something a basic amp may not be able to provide. I had a FiiO E5, and I really question if it was remotely enough. In the end, it really needs an amp. For the $170 price tag it initially carried (and I paid for), it really wasn't worth the price. At $99 it's actually a pretty good deal and definitely worth a look. It'll just come down to personal preference if you like it or not.
I think the PFE is more universally likable and has a little more initial wow factor. It also works better unamped, although it benefits well from an amp to keep the low end controlled and energetic.