Weapon Upgrades

Prefix:
1. Vampiric - Can't turn down more damage.
2. Zealous - Most Warrior builds can always use more Energy. Don't use it on Hammers though.
3. Elemental - For when you do have to beat on Warriors or other enemies with armor vs physical. Also good for your non-Vampiric swap.
4. Furious - A bit more functional than the two below. All functional Warrior builds require Adrenaline, but this gives a rather meager amount.
5. Condition - Hey, they're better than the one below.
6. Sundering - There is no reason to ever use this prefix above others, unless it gets buffed.

Suffix:
1. Fortitude - Better than armor in PvP, as more damage comes from armor-ignoring sources.
2. Defense - Better than Health in PvE, as more damage comes from many armor-affected attacks.
3. Shelter/Warding - A bit more armor than Defense, but in order to use them effectively you'd have to have two weapons.
4. Axe Mastery - It's an okay mod, but you generally get more use from Fortitude or Defense.
5. Enchanting - It's more for non-Warriors and some PvE solo builds, as Warriors shouldn't be enchanting themselves much.
6. Slaying - Only useful in certain PvE situations.

An additional comment to Savio's and Katari's posts:

As mentioned in my original post, axe warriors may find Furious mod more useful than Vampiric, since Axe spiking power highly depends on its skills (Axe has wide damage range). Skills like Eviscerate and Executioner's Chop are the core skills for axe warriors who will do great damage. But normal axe attacks will have slightly lower damage than sword (except criticals). It really depends on your playing style. If you will frequently use IAS skills, Vampiric maybe a better choice for you. But if your build has less than 3 attack skills (i.e. only 2 attack skills), then Furious may be better for you since you may want to spam skills more frequently (especially for axe warriors).

However, for sword warriors, as I've mentioned, Vampiric will be always better than Furious. Furious has much lower value for swords. Sword with Vampiric mod will have a constantly high spiking power, or even higher than axe.

Hammer warriors may not find Vampiric/Zealous very useful as their attack speed is slow. The health/Energy degeneration will be very unpleasant, considering you are already taking more damage than shield-wielders. Especially in PVP/GVG, your targets (i.e. casters) will always run around so the chance for you to effective use life stealing is relatively low. Sundering/Furious maybe the only options you can choose. However, you may prepare a Vampiric hammer and swap it when you are hitting your targets (but note the slight delay when you swap weapons, you may actually miss the chance to hit your target especially when your attack speed is low).

As for elemental mods, the extra damage done to warrior's armors (vs physical) will depend on the bypassed armor level (usually 10 or 20). If your target is using a reduce-damage shield, the bonus damage may not be promising. While on the other hand, Vampiric will constantly steal 3/5 health from your target foes, bypassing the AL. Therefore, I will say Vampiric is more useful than elemental mod.

However, if you are using conjure skills, then the bonus damage from bypassing certain armors + the extra damage from the conjure skill will do way much higher damage (usually 12 or more) per hit. It only applies to people who use conjure skills. The Enchantment Grip/Pommel may be also useful when you use this skill.

As for the Fortitude/Defense, Sword/Axe warriors should use Fortitude while Hammer warriors may want to consider Defense.

Take the following example:
For a 30 damage physical attack from a 15^50 weapon, the damage received by a shield-wielder
=(30*(2^((60-(80+20+16))/40)))*1.15 = 13.07
the damage received by hammer warriors (with +30 fortitude mod)
=(30*(2^((60-(80+20))/40)))*1.15 = 17.25
but if you use a +5 armor mod, the damage received will be
=(30*(2^((60-(80+20+5))/40)))*1.15 = 15.81

That means you are taking around 2 damage less for a normal 30 physical damage, the effect will be higher for higher damage skills. Therefore, Hammer warrior may want to use the Defense mod instead of Fortitude. It really depends if you are in Random Areans or in GVG, and if your opponent team which uses more physical/piercing/elemental(some has Armor penetration) damage or more hexes/spells.

As for Enchantment, it is on the 3rd place doesn't mean it is good. It's just there are not many choices left. In Random Areans, many W/Mo will use healing skills (which are Enchantment-based). Some W/E may also use Conjure skills which will find Enchantment mod useful. Of course, it is the most useful for casters who use melee weapons. Therefore, it is for sure the 3rd choice you can ever choose.

Shelter/Warding are not really useful in PVP as compared to Defense, considering of gaining 2 armor against either one of physical/elemental damage but giving up 5 armor of the others. Defense is always >> Shelther/Warding (except for PVE)

Weapon Mastery mod is almost the least useful since it is conditional (max 20% chance) and it is only effective when you are using skills.

Slaying maybe useful for certain PVE situations, but you may simply find Fortitude/Defense/Enchantment more useful instead of Slaying (except you have a collection of different slaying mods for switching, otherwise it is merely useful)

And Katari, many W/Mo does use Healing Breeze in Random Arenas. Even mending is still very popular. We all know certain skills suck at some point. But we cannot stop people from using them as it is their freedom. All we can do is to provide information and let them to choose according to their situation. Afterall, we are discussing about weapon upgrades but not skills. If you want to discuss about skills/builds, search a thread and post your comment there.