Style chooser

i recently visited a muffler shop in sunway and realised that i was spoilt for choice, there are just so many types of mufflers available. i already have an extractor and mid section installed (2.3) on my 1.8 putra. could someone tell me what i should be looking out for/consider before purchasing a muffler?
and what are the main differences between imported ones ($$$) and locally produced ones ($)?