I have tried several options over the years and am convinced the Littman Cardiology 3 is the best for me. I hear things that I did not hear with my old stethescope. I have had my current one for about 3 years and the tubing is beginning to split in one spot ( I have this nifty tape job on it). My biggest complaint is that I have not been able to find a place to just order replacement tubing, but they sell the tubing and ear assembly as one preassembled set and you just replace your bell onto it. They are fairly pricy at about $70.
If you do get a Littman, have your name engraved on the bell and label it every way you can and then never let it off your neck. They are hot items to steal. Yes, you may not think that your fellow students or others would stoop so low, but leave your scope laying around and see how fast that changes!
Edited to add: Sorry, I didn't know this was for CCU nurses, I am just an ER nurse, so you may disregard any advice I may have given