CNN have this article up today. If you look at the table on the right hand side, if they both get their way with taxes, McCain will help the middle class the most.

Income Avg. tax bill Avg. tax bill
Over $2.9M -$269,364 +$701,885
$603K and up -$45,361 +$115,974
$227K-$603K -$7,871 +$12
$161K-$227K -$4,380 -$2,789
$112K-$161K -$2,614 -$2,204
$66K-$112K -$1,009 -$1,290
$38K-$66K -$319 -$1,042
$19K-$38K -$113 -$892
Under $19K -$19 -$567