It really depends on the situation, using SA, using TA, mob, buffs you have, abyssea or not, etc. There are times when Evis outshines both mercy stroke and exenterator. Overall I've noticed exent has the most consistent damage when unstacked outside abyssea. Inside Evis almost always does better from RR. MS and Exent do better on very high def mobs.
Hate to say it but scroll back a few pages you'll see both compared a few times :)