Hey, I just did a custom cat back install on my 2010 Sport ram where I used a 22” SI/DO Magnaflow 5x11x22 PN#12588 with 2.5” pipe out the rear to 2 4x18 stainless tips deleting the resonators and it sounds amazing! It has a VERY deep tone, but not loud unless you step on it. Plus there is NO drone while cruising. One thing you should take into account is that a larger case muffler has more acoustical dampening in it and it will help reduce interior resonance so you will have less drone in the cab. If you go any smaller (like a 14 or 18" muffler) they have a 4x9" case and will produce a slight drone that you might find irritating when it drops int MDS.
Keep in mind... its all a matter of taste