The rules are simple. I'm taking in count a level 100 weapon.
0) first of all... I want to help people to avoid mistakes and maximize the benefits after spending their hard earned money.
1) looted: 3 direct damage, mana leech, lower defense and +20 SDI.
2) crafted:
exceptional (+20%base_dmg) craft with two direct damage and mana leech are mandatory stats, +20 SDI if you can, lower def if you can.
3) area hit: the two weapon above can have an area hit if you are very lucky with your drop/craft. For single target weapons the area hit is a personal preference, for WW weapons is a must.
4) auction weapons or weapons modified with auction deeds follow completely different rules. To get into this kind of "project" is better to know how the damage is calculated, how combat mechanics works, how many kind of deeds are sold on auctions and how to get the max from them... and you need to be rich, very rich

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Period.
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Part two: if you don't want to read the wall of text read underlined parts.
Now I want to talk about the 1H weapon obsession that hits a lot of new players on this shard. This send me back to point "0)": maximize the investment.
My next concern about investments is about the 2 handed weapons relayered into 1 handed weapons. But before i need to do a premise: what happens to block rate with
bushido and parry maxed? I see a lot of people with poor gear investing money into relayering their 2 handed into a 1 handed weapon because they believe that a shield gives more "defense". At the same time i see people scared to level bushido because doing this the parry chance will drop. Both statements are wrong. Worse: if you keep bushido low you sacrifice WW damage.
With a 2 handed weapon or a 1handed + shield you will parry the same exact amount of times. Tested! Remember: bushido 120 parry 130, both maxed. There's no reason to use a 1H weapon without shield. The test is pretty easy to do since the parry animation can't be unnoticed. Remove you DCI (full evasion) let a mob hit you 100 times and count the number of times you get damaged and the times you parries. Ignore evasions (you see no damage and no parry animation in this case).
Now that you know how bushido and parry interact on UOEX let's go back to our main issue. The investment...
the 1h relayer should be the last one, because you pay 1K ED (500ED to make the weapon 1h and 500 ed for the shield relayer) just to get the stats of 1 relayer. Let me reformulate: you pay 1000ED to gain 20HP/20SDI/half regens/half resistances/8 dex-str/16 sta, and so on, instead of 40HP/40SDI/double regens/double resistances/16 dex-str/32 sta. When you have no more slots to fill with relayers the idea of relayering the shield slot starts to make sense.
In conclusion if you know what I'm talking about and even then you prefer to build your set in a different way, maybe for the aesthetics, maybe because you like to roleplay.... remember: I'm not judging your playing style, I'm just trying to help new players to make their decision fully aware of the possibilities offered by the shard.