The weapon ratio alone is not what you want to go by to determine which weapon will be best for you. The quote below contains the formula most people use to decide if a weapon is an upgrade for you.
https://everquest.allakhazam.com/itemhelp.html Quote:
Comparative Efficiency:
A Meta-value designed to give a relative weight to the pure melee stats on an item. This is NOT a Damage Per Second value. This value is calculated with the following formula: (((damage * 2) + damage bonus) / delay) * 50. The goal of this value is to allow a rough comparison of a weapon's stats beyond simple ratio.
Offhand Efficiency:
A Meta-value designed to give a relative weight to the pure melee stats on an item. When wielded in the off-hand.This is NOT a Damage Per Second value. This value is calculated with the following formula: (((damage * 2) / delay) * 50) * 0.62. The goal of this value is to allow a rough comparison of a weapon's stats beyond simple ratio.
Your level will determine the damage bonus, and whether you use in primary or offhand will affect the numbers, but when i plugged in random damage bonus numbers it looks like the 20/17 ratio weapon will get you noticeably more dps in primary than either of the others.
Anyway, there's the formula you should use, and be aware that the values change as you level.