The curve helps with slicing, and straight blades are better at piercing, and both have been used by cavalry for thousands of years. The question which is better, has always been contested.
In RAW RQG there's no difference except with spears, but my group uses a house rule that two-handed weapons get 1.5 times the normal damage bonus, eg. +d4 rises to +d6 and +d6 rises to +d10.