A good build that is both powerful and relatively easy to use is the "RSC aquilla" or "RSC golem" if you are a member.
For the aquilla, the build is this:
Aquilla chassis
Reticulan Head/ oracle head
Armoured Arm
Turret Mounting
Rifled Sniper Cannon x 3
Plasma Spray x 1 / flak repeater / whatever
Scanner
two capacitors and one reactor if you're using spray, probably AMARDS if you have flak, have the rest with armor and shields and whatever else you find useful (maybe even missile scrambler)
The only downside to that build is that people will hate you for using it, as it is slightly overpowered.
The golem RSCer is basically the same, except you have nuke.
Another cool one is the GunQuilla:
Aquilla chassis
Reticulan Head
Thunder-Blade Arm
Light Shoulder Pack/Turret Mounting
fill up everything with miniguns and heavy guns.
Targeter, one capacitor, one reactor, and Aeruak Stabilisers.
One I like for city is, called the Rapierquilla (making up names

)
Aquilla
Reticulan Head
Multipack Arm
Shoulder Pack
Fill up everything with rapiers, then lasers where rapiers can't go. You might want to replace another one or two of the rapiers with more lasers, as they're quite powerful as well.
Then speed loader, aeruak stabilisers, targeter, and a capicator (maybe a reactor if you're a member).
I'll leave the strategy making up to you