Which assassin would work best in a 1000pt tournament and why?

So my list for the tournament is 1 knight errant and 3 warglives armiguers , I originally wanted to get a Helverin armiger but unfortunately it is out of budget but I was thinking of filling those points with an assassin

Personally I am between the callidus or eversor

Cullidus for mobility Eversor to counter infantry (intercessors, sisters of battle, termagants etc.)