I agree with OldManDave that the sprague rappaport is basically only good enough for taking BPs and telling if your patient has a heart... I think their popularity came from the show ER, where everybody seems to have one...
When I worked EMS we had them on the ambulances and, honestly, they sucked!!! Nobody at the ER, in the major level 1 trauma center we transported to, had one of those. All the docs and nurses had Littmans. Using the spragues, in the noisy environment we worked in, you could hardly tell the patient had a heart beat, much less make some more subtle but necessary distinctions about their lung sounds...In the ambulance they were useless even to take BPs, so we always had to use palpated BPs.
I have a $20 nurse stethoscope that is far better than the spragues we had, which cost about $30-$35. I didn't trust it enough though, to base my decisions on what I heard with it, so I bought a Littman Cardiology SE II and never looked back. I used it for several years and feel very comfortable with it, but it takes a while to get used to it because it has one of those pressure sensitive diaphragms, so I would also recommend that you get a Littman with a diaphragm and bell. Additionally, some schools will not allow their students to use the pressure diaphragm models.
When you become good at listening to heart and breath sounds, even a cheap $20 model will do, in a pinch, because you have fine tuned your hearing to pick up the sounds. But if you are trying to learn using the sprague, you will always be wondering why everyone hears the murmurs but you...