My normal preference is using rolz.org. Normally I prefer a simple 1d6 system I can up with for my events. Basically, attacker rolls attack first them defender rolls their defense. The higher wins, defender wins on ties. If attacker is higher, defender loses 1 HP. Defender wins, no damage. Then the rolls switch and this exchange goes until.someone loses three ho at which point they lose and rp out result. I find this to feel more organic and makes sure the fight is fair to both sides.
