Against killer robots, it's like trying to stop an unknown. How large is it? What's it made of? What equipment does it have? How well shielded is it? How many are you going to face?
You could have anything from something from 'toy soldiers' sized, armed with poison darts to an automated M1.
On average though, I'd want something full-auto, given that it's relativly easier to construct a device with multiple redundancies. Multiple holes increase the odds of something critical being damaged/destroyed.
I'd take AP. HP's are designed to expand in flesh, and work worse on machinery. Normal ball, in a rifle, isn't bad, but we're likely to have to punch through quite a bit of metal.
If it's a M1 analoge, though, I'll take RPG's, Stingers, etc.
Taking out a killer robot is the same as taking out any mechanism.
Damage types:
1. Computer/Control System, CNS equivalent
2. Fuel: Blood equivalent: Can be very slow. A bullethole through a fuel tank will make it loose power sooner, but that depends on the size of the hole, the tank, position, etc. Same as humans, bleedout can take days.
3. Engine: Heart. Robot may retain some capabilities without this. Multiple engines, etc.
4. Other mechanical damage: Everything from knocking down sensors(blinding), disabling limbs, flattening tires. Severing control lines from the computer can knock parts of the machine offline.
Strategy: Look for vulnerabilities, but overall, try to hose down the robot with lead and hope for all of the above. Afterwards, dissect to find critical points and better places to aim.