Sonar sensor questions!

Hi, I am working on a little robot for my arduino. I am going to buy a sonar sensor, but I found out that there were 4-pin and 3-pin sensors. Are they any different? if so, how? I really want to save a PWM pin for my RGB leds. Also, will this really work?

with the 4 pin, they have split the data lines to Echo and Trigger, instead of a single line. The 3 pin code will work, you just need to tweak it to work with trigger and echo. HINT: one is input and the other is output.