There's very diverse opinions regarding which weapon and armor to use in vindictus, most go for the logic of highest level = best and go Milletian, but gold/efficiency factor matters more.
This guide accounts the fact that R5 enchants will be released slowly.
I give a lot of importance into having everything +15 quickly and cheapest possible att limit, since more damage means more cores and enjoying your character to the fullest.
Here's the best combinations I could find:
Astera weapon, dullahan set: Strong in both s3 and s4. Your main character should start with this one. The worse compared to full dulla is the fact that it takes 3 times more myst shards to max att limit, but dulla can barely cap s4 so it doesn't matter much.
The idea is to use the 250 free steels given in what it seems to be a permanent event to upgrade the weapon, and if you're very lucky, use the remaining ones in the dullahan set.
This equipment will show its true power in brigid and s4 thanks to being able to hit the caps easily with its high att and extra crit. You will be able to go through the entire s4 with this and do max att limit dps.
Once you have a lot of spare gold, you can slowly upgrade helmet and pant to 105, always make sure you have enough abyssals to not lose att limit.
Best way to obtain: For the set, read "How to obtain +13 dulla", for the weapon I don't suggest upgrading it yourself because you will waste runes, and runes are very limited in early game. Either wait for an event that gives +11 coupon or buy it from marketplace (+12/+13). Note that in s4, the steel cost of astera goes down by -25%.
Required grade 1 shards for max att limit: 360 myst shards and 75 abyssal shards
Astera weapon, milletian set: If you reached this point it means you're sitting on a mountain of gold or you're a whale. I highly suggest to not start with this build, you want to have a maxed dulla armor set first, then slowly upgrade the pieces to 105. This is a very strong combination since it will have huge defense stat as well as access to R5 enchant scrolls (theorized to give a total of +10 crit +10 bal in armor once all of them comes), and the astera weapon caps everything with ease thanks to the crit boost of the R5s.
The downside of this build if it wasn't obvious already is the terrible high amount of gold needed for the 105 set, it starts at low rolls, synthesis is very expensive, R5s will probably be expensive, and needs nearly 5 times more abyssals than dulla.
Best way to obtain: For the weapon, read above, for the set the same applies, you don't want to spend runes so buy it preenhanced.
Required grade 1 shards for max att limit: 360 myst shards and 360 abyssal shards
105 weapon: Crazy expensive due the fact that it can't use the 250 free steels, but its high crit means being able to place calm dash at once and future proofing you by crit caping on the new s4 bosses. Go for this after finishing helmet and pant milletian.
Full dullahan: Strong in s3, weak in s4 without major investment. I only recommend this to alt chars that don't plan on running s4 without trans. With your main you want to replace the weapon as soon as possible.
The idea of full dullahan is to max your add damage very quickly with the lowest possible amount of gold.
How to obtain +13 dulla: Do all the main quest, you will be provided with jumper stones to make the weapon +12 and the set +13. With a rune that costs 95 seal of bravery, you can make the weapon +13.
Last thing to talk about the free dulla gear is that the game gives you the choice to either craft your own gear or use one given for free with full R7 and max rolls. The one given for free can't be dismantled. This means if you upgrade its att limit, the shards are permastuck in that gear. The only way to retrieve the shards is to leave the gear at +15, and use an extraction rune (NX shop) while attempting +16. On the other hand if you craft your own gear, you can make them 3 stars and preinfused, but you will have to synthetize and enchant it yourself. Personally I would craft my own for my main, and use the free one for my alts.
Required grade 1 shards for max att limit: 120 myst shards and 75 abyssal shards
Now will comment the non-viable gear:
90 weapon: Trash, complete trash, has the highest balance of all weapons but that means nothing which such low att and crit.
90 set: Aside of the low def, the most important aspect is that it can't wear R6s, which is a big downside. However, 90 sets still have an use! when you get the +12 set you can try to +15 it to get an early add damage boost. If you get one or more, you want to +15 the rest of the dulla set before replacing these lucky 90 pieces.
Astera armor: Probably the worst offense regarding endgame gear, all this armor set does is giving +2k def +20 res over dullahan at the cost of needing 225 abyssal shards and 3 times more steels. Can't wear the upcoming R5 enchants either. In my opinion this set was created as a gold sink to lure people into it. Its not even cheaper than 105, since a 105 piece gives nearly the same def as 2 astera pieces, plus R5 slots, for the same amount of gold. Seriously, don't make this.
- Dullahan set makes you die very quickly to low def: False, if you play a char that can't tank you will not notice the difference, if you're playing one that can you're gonna need to use pots no matter which set you use. Dulla can reach 24k def in normal raids, which is more than enough.
- Weapon stats is all that matters!: False, in vindictus the most important is reaching the stat caps of the bosses. To put you in perspective, neamhain has very low caps, so a lv90 weapon will deal the same dps as a lv105 in there. Its very important to planify your stats to reach those caps, and which bosses you prefeer to focus on.
Hope this helps you deciding which gear to use. If I was you I would start with astera wep, dulla set, then upgrade helm and pant to milletian, and then weapon to milletian.