I have both, and honestly, they're both good steths. I personally prefer the MDF, but the MDF is kind of heavy. So if you're the neck-wearing-steth type (I am not), I'd go with a Littman. II SE is a good one for nursing school. Classic III is more sensitive but more expensive.
Keep in mind:
While you want a good steth for nursing school, you won't want to spend bank because of all the abuse it will take. Plus the risk that it will get lost, stolen, damaged...
Even though you say this one will go into your career with you, once you graduate, you will have the desire to treat yourself to a really good steth, likely engraved with your name and RN or LVN. So you may not want to go overboard with the nursing school one.