Mario's Cape - 1 vote
Peach's Toadstool - 0 votes
Link's/Toon Link's Shield - 0 votes
Pit's Shield - 2 votes
Fox's Energy Shield - 0 votes
Falco's Energy Shield - 0 votes
Wolf's Energy Shield - 2 votes
Lucario's Counter - 0 votes
Marth's/Ike's Counter - 1 vote
Ness'/Lucas's Energy Absorber - 0 Votes
Zelda's Nayrus Love - 0 votes
Mario's Cape: Stops all projectile (including PK Flash and PK Freeze) and physical attacks. Not resistant against transcendent priority, such as z-air (Samus, Link, Toon Link).
Peach's Toadstool: Counters all projectile and physical attacks, including transcendent priority, but is useless after it has been out.
Link's/Toon Link's Shield: Stops projectile attacks, but only if Link/Toon Link is standing. It's also dependent on whether or not Link/Toon Link is turning his body or doing some sort of movement.
Pit's Mirror Shield: Stops all projectile (including PK Flash and PK Freeze) and physical attacks, including transcendent priority. Projectile attacks increase in speed and power once reflected. It also acts like Mario's Cape when the shine is present when it is brought out.
Fox's/Falco's/Wolf's Reflector: Reflects all projectile attacks, including PK Flash and PK Freeze. Projectile attacks increase in speed and power once reflected. Reflectors can be used as attacks as well. For Falco, projectiles are reflected until his Reflector is put away. For Wolf, invincibility frames at the start-up.
Lucario's/Marth's/Ike's Counter: Counters all attacks and projectiles. For Lucario and Marth, the cool down leaves them open for attack while they're still in the last frames of Counter. For Ike, it's the opposite. His start-up leaves him vulnerable to attacks. It takes a bit longer.
Ness'/Lucas' PSI Magnet: Absorbs all energy-based projectiles, including Zero Suit Samus' d-smash, PK Flash and PK Freeze, but it's not resistant to solid projectiles or physical attacks. For Ness, the PSI Magnet gives a small push, but it's barely noticeable, let alone useful. Ness can also get out of his PSI Magnet instantly after absorbing energy-based projectiles. For Lucas, the PSI Magnet can injure his opponent. He may also use it to recover after perform PK Fire and the PSI Magnet away from the stage, which pushes him toward the stage.
Zelda's Nayru's Love: Reflects all projectile attacks, including PK Flash and PK Freeze. It may also be used to injure Zelda's opponent. Projectile speed and power also increase if reflected.
I'd have to say that Pit's Mirror Shield is the best defense. Link/Toon Link has the worst.