I've heard the opposite - the oval is meant to have a really nice tone not quiet but not overly loud either - just right. I'm get the twin 3" outwardly rolled sportex just after xmas. I like dearings 3" which is the single version of the one i want. The single 4" does look nice aswell.
I think either the single, oval, or twin would look nice, but I've got a 4" round so I'm probably likely to be a bit biased. Mine isn't stupidly loud but it's got a nice deep tone to it, but mine's a Powerflow backbox, which nobody has mentioned here yet lol.