Choosing rangefinder for obstacle-avoiding
Odds are pretty good they are real close. I've only used the sr04 with
  4 pins (too lazy to mod) and it was ok. cant say if the parallax is
  better or not. For 4 times the price you'd expect it to be, but so far
  in robotics, price seldom reflect performance in my experience. – 
  Spiked3


I've also used the SR (with 4 pins) and it worked great. &lt;2$ on eBay