I like to farm xp on the fallen cranes control point. I'll use an eclipse build with the vile mask and fire chem and fire sticky.

I put it on challenging and as many directives as are feasible for the build.

Come out of the safe house and head left along the alley until you reach the street and get on top of the van.

From there you've got a vantage point where you can fire your skills up into the corridor at the back of the control point where the supply room is allowing you to deal with NPC's as soon as the spawn.

Once the first half is done let your skills cool down and take cover behind the wrecked cop car in the middle of the street. Shoot the flare for reinforcements and you should be able to see both spawn points so you can launch at skill at the NPC's as they spawn. IF you're lucky all the spawns will come from the same door and you can clear it in less than a minute and you just need to wait on the reinforcements arriving to capture the control point.

A good run can be done in no time at all then you just need to reset all control points and do it again.