Triangle
What would you recommend as the Rate and Amount? I tried Triangle but it doesn't seem to do the ping pong effect.
What do you mean by ping pong effect? Triangle will make it bounce from side to side back and forth and Square will make is jump from side to side, set a good amount (100+ to really hear it i guess) and adjust rate to taste. If you can't hear the back and forth maybe check that your soundcard is set to stereo pairs and not individual mono ins making everything mono.
To hear this better make a tone that is constant and apply the effect. Set the pan to centre to begin.
edit - Also maybe check your mod matrix that something else isn't effecting the LFO rate throwing the consistent left-right-left off. Also rate wise if your not using "sync" amounts between 1 - 100 are nice then after that it gets pretty fast heading into audio rate range. I can record what i get when i do this if your still not getting what you expect so you can hear if things are right.