The Sportster muffler is only kinda loud.  A nice, mellow purr that makes it sound like a real bike instead of a lawn mower (like the stock muffler).  If you do a bunch of drilling, and don't like it, you're stuck.  My stock one was too rusted to put back on.  Get a Screamin' Eagle if you want it to be really loud.  

Either muffler should be cheap, so you can play with what works for you.  Try www.elvisplace.com for cheap, decent stuff, or ask real nice at your local Harley dealer.  They probably have a whole pile of takeoffs.  

As long as I wear earplugs, the SE is fine.  Don't know what the neighbors think about it.  I try to stay off the throttle until I'm a few blocks away.