The ER4 I have is the S version which does not come with the new braided cable. I don't find it very hard to walk around with them as long as I have it clipped to my shirt/jacket. With the e3cs, you will not run into microphonics (as with the Ety's), but there are other downsides to having it behind your neck.
1) When sitting down sometimes the cable (which is behind you) pulls down which is quite uncomfortable. I found myself readjusting the cable frequently so it wouldn't pull down on my ears.
2) There is this weird "under the arm" type maneuver that you must do to wear the e3 properly. It requires you to fling the cable around your back, under your arm, and then tighten the cords at the Y intersection so they don't move around. This is surprisingly very unintuitive compared to the Etymotics. This is pretty hard to do while sitting down and it takes a fairly long time to get setup.
3) The cable isn't fastened to your clothing. This means when walking, the cable will flop around and possibly get pulled and cause discomfort by inflicting a force on the ears.
4) When stitting down, sometimes you do not have enough slack on the cord located above your upper back, and the cord will pull on your ears or restrict head/neck movement. This is really annoying.
I ran into these issues constantly with the e3c and in my opinion, the microphonics are worth it to not deal with these issues. Now, with regards to sound quality, I already went over this. The e3's are not even in the same league as the ER-4's. The sound of the latter completely trumps the former.