My favorite exotic weapon is pretty easy for me to pick, seeing as I only have two so far. However i think that it would be the Super Good Advice machine gun, thing is a beast. With decent fire rate, high damage, and the bullets that go back to gun, this thing is formidable. On pve, wait for a group of vandals and such to run up, spray and pray. I love doing it. Also when you're fighting a boss at mid-range, doesn't hurt to pepper them with burst fire. On PVP I just find a well traveled route, traverse it and rack up some kills.