Actually a weapon that tired you after a few swings is a bad weapon. You want maximum damage with minimal exertion. Most viking raiders weren't full time soldiers. They were mostly farmers of some sort back home. So they used gear fitting a farmer and commoner. They used spears and axes. Axes were tools from everyday use. If they had the money they used a axe fitted for combat with better balance but any axe is lethal.

Spears are always popular because unlike a sword or axe there is little to no edge alignment. A spear is one of the easiest weapons to wield somewhat succesfull. The iron of Scandinavia wasn't the best so big pieces of high quality metal was expensive. This made swords rare, it made two handed weapons even more rare. Pretty much any warrior who used a dane-axe or a two handed sword had to be professional warriors. Contracted by a rich local lord on top of that. I expect those men to train extensively by the very nature of being a professional soldier. Unlike the raiders he was paid to fight every day and not just during a few weeks raid.