I just bought a basic $20 package with a scope, scissors, pen and such when I started nursing school in 2000. It worked for me. Generally, the more you pay, the better they are. Litmann makes a great scope. I have bought 2 - and both grew legs and walked while on clinical or at work. I currently use my $20 special and it works fine for me. As for length, generally, the shorter they are, the better you can hear.
Best of luck in your career.
Craig