In an epic level game, assuming you don't fight a lot of undead/constructs/other crit immune enemies, improved critical threat range/multipliers are almost always better then an increase to damage.

For example, at low levels a longsword is usually better then a rapier. assuming 14 strength a longsword averages 6.5 damage while a rapier averages 5.5, thats a pretty significant increase (almost 20%). The 5% greater chance that a critical threat will be rolled won't give you that much extra average damage.

In a epic level game where you are doing 50, 100, or more damage per a hit, the extra 1 or 2 damage from a larger weapon doesn't matter. Damage points don't scale to level, but criticals do. As your damage per hit goes up, the amount of extra damage the improved criticals grant you does as well.

From a math standpoint, an increase to threat range and an increase to multiplier is almost identical, for example, a longsword will add 100% damage to your attack twice as often as a battle axe, but a battle axe will instead add 200%, it evens out. I prefer high threat ranges, but thats because I like my weapons more reliable.