Napalm: Good for making defensive lines. (Say you are capping A, you can make a wall of napalm between you and oncoming enemies.) Also stays and may burn people who accidentally touch it.
Percision: Larger explosive radius. Can take out many enemies at once easier. Can clear out maves and destory ground based killstreaks easier.
No question. Napalm. I am fairly certain that Percision Airstrike does little more than make fireworks. Very rarely do I get the pure rapage I should get with 3 F-16 Tomcats flying over dropping each a full payload. But you know, got to make that freaking Stealth Bomber worth something.
Never forget the time I got 4 napalms saved up and burned the whole of Nuketown, killed every player 3 times in about 15secs 
