Maganflow is really nice, especially for the money. They are completely stainless steel so will last pretty much forever. They are all also "straight through" designs, which means basically no restriction what so ever, look at a cutaway of a magnaflow on google you'll see it is basically a straight pipe. The magnaflows have packing that will burn up after a while, so they will get louder, so if you start with the 18" in a year or two it will probably be as loud as the 14". I plan on getting an 18" because I don't want it to be too loud in a few years... The only other mufflers I have experience with are flowmaster, and they sound decent, but are somewhat restrictive and rust fast.
Breathing in and out is good enough for me.