How do you define top weapons? Obvioulsy if you go just by stats, Plains level weapon will obviously be the best ones...
So I am going to go by a different metric.... how useful is the weapon both in its own as well as later biomes?
1. Iron Mace - not only it is the king of the Swamps, it remains the best weapon for fighting Golems in the Mountains and Growth in the Plains.
2: Draugr Fang - despite being only a Mountains-tier weapon, it remains the best bow in the game simply because there is no Plains-level bow. And bows are quite useful in the Plains so it definitely has a place on the list.
3. Iron Sledge - pretty much the best area weapon until the Blackmetal Atgeir two tiers later.
It decimates everything in the Swamps, even allowing you to kill enemies behind walls and scrap piles without even having to fight them. It is also excellent for dealing with hunt invasions in the Mountains while using Bonemass power.