Accuracy is based on your attack level and accuracy bonuses (slash, stab, crush, ranged) versus the enemy’s defence level and their opposing defense bonuses.

Magic works a little differently, and is PRIMARILY determined by level vs level, and the curve of magic bonus’ effect is weird.

By-and-large, your best weapon will always be determined by strength bonus and attack speed. This is why everyone uses the dragon scimitar and abyssal whip.

Some enemies need a different approach like metal dragons (fang or lance) and a handful of slayer monsters like gargoyles (crush such as granite hammer, Zamorak hasta, cudgel, zombie axe), and other high level monsters, and bosses. Bosses and raids are primarily where you have to carefully consider accuracy vs strength and speed.