Torch is a condition damage weapon (in guardian's case it'a all done by "burning" condition) while focus is more of a utility choice (it gives you some decent damage and a great shield with skill #5)
When making a dps or solo build in this game the first thing you need to ask yourself is if you want to do condition based damage (basically damage over time) or power based damage (direct damage)
This will change which stats you use on your armor and weapons.
Power (damage), precision (crit chance) and ferocity (crit damage) are the most important stats for power damage.
Condition damage and expertise (condition duration) are the stats you want to focus on if you want to do condition damage
Based on this choice, you can more easily choose the right weapon for your build.
Now, coming to your actual question, you can build both core guardian and dragonhunter to go with power damage (in which case I'd go with greatsword/sword + focus)
If you want to build condition damage, core guardian should be better at it (best weapons would be sword/torch and scepter/torch).
This being said, for open world you can experiment freely. I too often use focus over torch in any case because it's more comfortable having a shield and being able to blast fields.
Also if you're new I think the extra defense could be more useful right now