I had the same dilemma a few weeks ago, so I started a poll:
[AND THE WINNER IS...] Which IEMs would you buy today as best sound isolators?
Today people is still voting and the Etys go first in the count. And if you add the 4P + 4S votes they take almost half of the votes. I chose ER4Ps and I'm extremely satisfied!
Also for the U.S. 4P's price at $169 you can add a P-to-S converter and have two headphones in one for the price of the SA6. That was a big plus in my decision, but honestly, I think they're head to head. I didn't like the idea of changing the little pieces according to the signature, but probably that's something that people love about the SA6. I decided for the Etys mainly because they're the best isolators and almost in any poll or question people put in this forum they win, even against more expensive IEMs like the Shure 530. Check the following threads:
Etymotic ER4 closest to perfect?
IEMs that decisively beat ER-4P at ~$180 and below (for iPods)
Best IEM for acoustic music: Ety ER-4P / UE Triple Fi / Klipsch Image / Shure SE530?
That's my $0.02. I'm a new Ety's fan
