ULTRASONIC Receiver & Transmitter Prob ?

HI, I'm making ultrasonic range meter project.

So i wanna buy Ultrasonic ( 40KHz ) Transmiter and Recever. I search it on a FARNELL.
There r lots of products. And all fo those speakers has Capacitance. Like 1900pF , 2400pF.

So this is my question. Wich one gives me the best results ?

parallax makes a ultrasonic reciever detector called PING))). Go to https://www.parallax.com/detail.asp?product_id=28015 and check it out.