Like a scout sniper. From as far away and as hidden as possible with very high calibur weapons and be accurate with headshots.
The Dart Gun is a must. So is weapons like Lincoln's Repeater, The Terrible Shotgun or a Sniper Rifle.
(On Very Hard)
-Detect them early, max out sneak to level 100 and keep your distance -Dart gun is a must -Use high damage weapons
Vengence (Big guns) Blackhawk/Callahans/SniperRifle (Small guns) A3-21/Gauss rifle (Energy weapons)
-Use chems with Chemist, and Chem resistant
Psycho (+25% Dmg) Jet (+40 AP) Med-X (+25% DR)
-High Critical hit %
Lucky 8 ball (+1 to luck) 10 Luck (+10%) Survival Guru (+3%) Finesse (+5%)