The 2001-2003 1200 will interchange if you get the midpipe with it. The 2004-2005 1200's muffler is welded to the midpipe, like the 600, and it will interchange, too. I'm not 100% sure if the 1G's muffler OE mount is in exactly the same location, but I
think it is, if so, you can use the 1G 600 muffler, or the 1200's if you get it's midpipe. The midpipe/muffler DO NOT interchange between the 1G and early 2G B12's because the mounting flanges are clocked differently.
When it comes to aftermarket cans, you can use any B12 can that comes with a midpipe. You can use aftermarket bolt-on B12 cans if you have the corresponding B12 midpipe.
When it comes to the sound of an aftermarket can, I've yet to hear one that sounds like a Civic with a burned out muffler.
Different brands may have different sounds - in tone and db. My own persoanl tastes lean towards the Yosh & Holeshot cans.