The best armor are the mastercrafted Feline/Griffon/Bear sets.
The best weapons are the ones with Burning/Bleeding/Poisoning chance as the damage they produce is based off of the total HP of the monster.
If you can find a three rune slot sword with +xx% of Burning, Bleeding and Poisoning, then it will be a good weapon way past it’s level. Hell, even two of these in any combination will be a good weapon for a long time.
I used a level 16 sword all the way until I was level 24 because it had a Bleed and Burn chance that I kept increasing with runes. Every 3-5 swings would put a DoT on the monster.
The Mastercrafted Witcher Gear is only relevant up to level 31. After that, generic gear scales with you while the Witcher gear becomes obsolete. The ursine Witcher gear gives you good tanking armour but sacrifices stamina, griffin gear is a good to give good protection while not sacrificing much stamina, and feline gear is best for low damage absorption but little stamina loss.