hard to judge without knowing your skills and choice of weapon, but i myself use a Xent X3 with A102 amp. The Mirath Fatal Shot with A102 is stunning for eco and range but cos its Toulan its usually uncommon to come across, so i usually go get my own when it breaks.
ideally something around the 10-18 dps (low side is good for rifle, but i'd aim on the higher side with an handgun or melee) with best eco you can obtain. remember to use a finisher, the S1X1 Chon is perfect for this