DRG is great. Are you thinking of getting a Cardiology steth? I find that the DRG Cardiology models are better than Littmann Cardiology models, in terms of sound clarity. I find that the Littmann tunable diaphragm creates some artifact which especially makes splitting and gallops hard to figure out.
The DRG cardio models have thicker tubing than Littmanns, which really makes a difference on the ambulance. Lung sounds will not sound strangely similar to a diesel engine, with the thicker tubing. The DRG tubing also has non-slip bands on the tube, so when its draped on your neck while youre working an arrest, it wont slip away and land under someones boot. However, DRG is pretty expensive, making it a lousy choice for me.
You don't really need a Cardiology scope, A Littmann Classic or equivalent would be just fine. But for me, the ambient noise reduction of a cardio scope is worth the price.
I would really reccomend an ADC Cardiology scope. It is just as good as a Littmann, for a fraction of the price. You can also choose one without a tunable diaphragm. I used an ADC as a medic, and got a more expensive, fancy scope for medical school. When I go back to EMS, or am working like a nut on the wards, I prefer the good ol' ADC.