Whichever one you hear well with and fits comfortably in your ears. While I whole-heartedly recommend dual-lumen steths, other than that I'm the anti-stethoscope snob. If you're good at using it, it's because of what's in between the earpieces that's most important. The external equipment is one of comfort. If you truly are hard of hearing, then check out an amplified scope, but most people with normal hearing that I know, have not liked using an electronic scope for the sake of it picking up too many extraneous sounds (e.g. lungs sounds while listening to the heart). I have been using my Littman Cardiology III since 1st year med school (now 9 years ago) and use it one anyone from premature infants to adults (as a pediatric cardiology fellow). There are other stethoscopes that are probably just as good (lots of people like the Harvys). I've been interested in trying the Magna Fortis scopes (http://www.stethoscopes.com/)-based on their claims-but haven't gotten around to it.