The dirt guys say "DIRT", while the asphalt guys scream "ASPHALT". With the economic shape that the country is in, and the effect that it has had particularly on the local racers, what the best way to get into racing has in large part taken a back seat to what costs the least.
This article from a 2009 issue of Stock Car Magazine takes on driver development as the primary issue in deciding which way to go, and provides some things to think about when you make the descision.
In the good old days, it was simply assumed by everyone that if you wanted to make a living racing in NASCAR's Nextel Cup Series (then called Winston Cup), you needed to make a name for yourself racing and winning on asphalt tracks. After all, Cup races in the sport's modern era (since 1972) have been held on paved tracks, so that's where you needed to race. It only made sense.
Of course, that all went out the window in the mid-'90s when Jeff Gordon and then Tony Stewart came on the scene...