Question about PSU specs

[LeetestUnleet]

See below for the PSUs I'm debating between.
Questions:
What is PFC?
What is Hold-up Time? Is a higher or lower score better?
What is Efficiency % rated on?

Antec P4 ATX12V 400 Watt Power Supply With 2 Fans, Model "SL400" -RETAIL
$58 shipped

PFC: No
Hold-up Time: < 17ms at Full Load
Efficiency: >68%

Antec 380W Power Supply, Model "TRUE380" -RETAIL
$67 shipped

PFC: No
Hold-up Time: > 17ms at Full Load
Efficiency: < 68%