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tl;dr: Equip a weapon, check your stats. Equip another weapon, check your stats. Pick better stats.

Weapons that are above your current rank slowly scale up to their full stats, so at times they can be better than a weapon that has an optimal rank below your rank, so the only real way right now to see what is better for you is write down your stats and switch between weapons to see which is better.

Example:

For Weaving, I used a Bronze Needle (optimal rank 7) until about 13-14, where the Iron Needle (optimal rank 22) began giving better appropriate stats.

Now I'm rank 26 using the Iron Needle(R22) that puts my craft stats at 40/38/33 and I have a Silver Needle(R32) that puts my stats at 39/37/33, so it currently is a worse option. However, once I hit 27-28, the Silver Needle will scale up a little closer to its listed stats, so it will likely become the optimal tool.