The Pinger can be a very hard machine to understand at first, but soon enough, you can [ut it to very good use. I'll explain all the attacks and best uses for them.
R1 is a laser cannon that can reach a very fast rate of fire point, as well as have a lot of damage behind it. However, it has no accuracy behind it, as it spreads in a "broken glass" method (just thrown around everywhere), so the best use for it is to slowly shoot it one by one, speeding up the closer they are, but never reach faster than tapping R1 then saying "one" then pressing it again, otherwise you may miss your target by a long shot.
R2 is a missile that has a very good explosion radius. Now its best use is to shoot it before and enemy goes around the corner or if they are a long distance from you. Should they be cloaked they will have no chance of escaping it.
R3 (clicking the thumbstick) lets out it's ping attack, which is a huge close range shock wave around you. Now the best time to use this is when an enemy is very close to you and you can't hit them with your cannon (but only when they are on the same level or a level higher than you), or when they try to board you. It's a one shot for those who dare to go into its zone, no matter what armor is on.
Best map for going for the trophy: Financial District
Financial District is great for you because it is a very tight but vertical map, and any attempts to try and board you would be extremely easy to catch due to the camera pretty much zooming on the top of the Pinger. As for the tight quarters, it means that there is a chance that they won't look on their radar and won't see you until it is too late!
Best game mode: Crash Site/Spears
In this game mode, once you have the Pinger, not many people will go out of their way to get you, for the most part they will try to run by to capture the objective, so utilize that as easy pickings.
Good luck with the trophy!