mufflers:which is better!? please help

ok my 1979 el camino has a stock muffler and i want to get maybe a flowmaster 40 series are those any good?! or whats better i want it to rumble but be street legel? well i noticed on the exhaust pipes are rusted too would it be wise to get new pipe while i get the new muffler or doent it matter?

ok my 1979 el camino has a stock muffler and i want to get maybe a flowmaster 40 series are those any good?! or whats better i want it to rumble but be street legel? well i noticed on the exhaust pipes are rusted too would it be wise to get new pipe while i get the new muffler or doent it matter?
I would probably go with a Magnaflow - I heard that Flowmasters don't flow as well compared to other straight-through mufflers.

As long as the tube thickness isn't too low, rusted pipes should be fine.