The things that will be the biggest increases on your damage for the least merit investment are Crits and Skill.
Way back then when i merited WAR, i went with 1 skill, 1 crit, 1 DA, 1 Zerk, 1 Agg. Then i repeated the process until something got where i wanted it.
I think it was probably one of the most efficient ways of getting the most out of your merits quickly...