Despite the heavy metal and rock emphasis at the top of the charts, Anita Baker's jazzy ballad album continues to be the nation's best seller. Another woman bucking the hard-rock trend: Edie Brickell. If Tracy Chapman weren't everyone's choice for best new artist of 1988, Brickell's achievement might be getting more attention. Her album, "Shooting Rubberbands at the Stars," is filled with oddball, poetic rock--the kind of album that usually languishes in the lower depths of the Top 200. Remarkably, this one (No. 16 this week) appears headed for the Top 10. Another female, however, may be in trouble. Tiffany's "Holding an Old Friend's Hand" is slowing down, moving up just one notch this week--to No. 19. The new No. 1 pop single is Bobby Brown's "My Prerogative."