Actually, a 3x3 or 5x5 door on frames/pistons (wtf do you make a 5x5 redstone door seriously)/turtles looks much better than a double door. If you're making a bridge, like...
U = Block
G = Nothing
GUUUUUG
GUUUUUG
GUUUUUG
GGUUUGG
GGGUGGG
GGGGGGG
...this, it looks nice.
But with this...