While it's hard to go wrong with a Littman Stethoscope, there are others that are very good as well. ADC makes some good ones. Ultrascope is one I've not personally used but I've had some co-workers absolutely swear by that brand. In my case, I'm able to effectively use pretty much any stethoscope from the $12 cheap models on up... but I'd advise finding (and using) really any mid-range ($20-$50) dual-head (diaphragm and bell) model and use that while learning. As you get better and more proficient at listening to body sounds with it, you'll find yourself figuring out exactly what kind of stethoscope you'll need as you advance in your practice as a Nurse. My own stethoscope is so good that I can almost hear a mouse toot from across the room... those electronic gizmos will do the same from across the hall and down the block. In my last rotation, the pedi head of the steth was so big that in some places on a newborn's chest, I could hear a heartbeat and a very strong pleural friction rub. I had to move the head out near the shoulders to hear actual breath sounds. In that environment, an actual neonate head would have been better, as I wouldn't have had to move the steth head that far and it would have been easier to maneuver.
My own personal stethoscope is a Littmann Cardiology III. It works for almost everything I need... but it's not exactly an inexpensive unit. I've also had mine for >10 years. If I were going to be a NICU/L&D/PP nurse, I'd go for a stethoscope that is specific to neonates. As it is, I haven't had much of an issue with the steth that couldn't be worked through.
That's my personal preference based on my own experience, and your experience will be different from mine. You'll come to your own conclusion as to what's best for you and your specific situation soon enough!