Combat skills are the best merits to focus on for any melee job - missing less is just huge. And theres the bonus atk in there. They wont raise your SAM WS damage, but they will improve all your other damage.
Atributes should be your last merits for ANY jobs. They cost too much, and the bonus they give is very small compared to anything else.
Particularly for SAM, Overwhelm is huge. Still not as great as raising combat skills, but certainly much stronger than STR.
The hardest part of this game is finding 5-17 other people who aren't retarded.