Well They both have there uses, but......
Javs & shield do not suffer the -1 from moving and do not suffer the -1 "over half range penalty" because of throwing. So there reach is 14 inch (with the 6 inch move) They hit on a 4 and poison on a 6. The skinks recieve a 6+ save vs shooting and a 5+ save CC (handweapon/shield) and even a 4+ when playing with a Sacred Spawning of Quetzl list....Thats not to bad imho.
peashooter has a range of 18 inch (again with the 6 inch move) and will give you more shots (with the multi-shot). But when moved you hit on a 5, Multi-shot makes this 6. This means you will have to be within 6 inch of the enemy, otherwise it will be hit on a 7+ (first a six then a 4) but that no poison for you....
So thats more shots but only on a 6 you hit (and poison if within half...) This makes it's effective range 12 inch vs 14 of the javs)
Most of the time i use javs & shield on field skinkies, and peashooters on scouts...
What's best....that depends on your playstyle.......
well that's my $0,02