I mean, with Amber it was 'best rank wins, unless you cheat'. And let me tell you, did my character construct a lot of cheats... Enough to attack two players in a 1-on-2 while countering everything they pulled and having the GM basically spare them and give them several chances to just run away already. So if you want to leave it to the GM less, you'd need a system that puts a mechanical impact to the 'generating a difference'. For example, a system I know for a LARP gives a +1 rank to an ambusher, and the attacker wins on ties.