The very worst old uniform is the original Tampa Bay "Gay Blade" look, and the pink motif that came with it. The team has improved significantly since they switched to the Jolly Roger pirate look.
But the Steelers Bumblebee look is a close second. I would point out that those uniforms worked well in the days of black and white television, when the stripes were the only way to tell who was who on the field. Color television eliminated the need for the extreme contrast necessary for black and white broadcasts.