First of all, you need to know that dex scaling is pretty wonky. There's not much benefit between an A and S rank. Keep that in mind.
Also note that poison and bleeding scales with DEX.
The weapons with best DEX scaling ( A/S ) are:
Ricard's Rapier (starts with A scaling, gets S once upgraded to +5) - Huntsman's Copse. Bottom of the pit after first bonfire.
Rare drop from Spiders in Brightstone Cove Tseldora.
Curved Dragon Greatsword (S)- Trade Ancient Dragon Soul with Ornifex
Hunter's Blackbow (S) - Found in the chest down a ladder at the second bonfire before the Dual Dragonrider boss at Drangleic Castle.
Mirrah Greatsword (A) - Buy from Merchant Hag Melentia in Cardinal Tower or Majula after killing Lucatiel. Given to you in Aldia's Keep at the first bonfire by Lucatiel after following her storyline.
Warped Sword (A) - Trade Flexile Sentry Soul with Straid of Olaphis
Espada Ropera (A) - talk to Chancellor Wellager in Drangleic Castle after defeating the Giant Lord to receive the Espada Ropera and the Royal Dirk.
Caestus (A) - Purchasable from Merchant Hag Melentia
Parrying Dagger (A) - Located in a chest behind a boarded up wall closest to Cell bonfire in Lost Bastille head left from the bonfire and head up the stairs and down the rampart. Go down the ladder to your left and go through the door way and head right. There will be a boarded up door. Break the boards and head through and to you left. You will see a door. Use the Antiquated Key to open it and head straight and through the doorway, climb up the ladder to your left and drop down onto the raised platform. There is a passage way that leads to 3 chests. It resides in one of them.
Spider Fang (A) - Trade Soul of the Duke's Dear Freja to Weaponsmith Ornifex
Uchigatana (starts with B, gets A on +5) - Purchase from Steady Hand McDuff
Washing Pole (starts with B, gets A on +10) - Dragon Shrine (Chest) (Mimic)
Chaos Blade (starts with B, gets A on +5) - Trade the Old Witch Soul with Ornifex
Blacksteel Katana (stats with A, gets S on +1) - Dropped by Alonne Knights at the Iron Keep
Manslayer (starts with B, gets A on +5) - From the rise of the dead bonfire in the Shrine of Amana go up the stairs enter the door. Make sure you are hollow and you rescued all sirens or the door will not open. From there continue along the path and through the shrine room and down the next set of stairs. Now go outside and take a left and walk along the ledge. The katana will be inside a chest to your left near the wall.
Darkdrift (starts with C, gets A on +10) - Talk to Grave Warden Agdayne in the Undead Crypt after obtaining the King's Ring.
Murakumo (starts with B, gets A on +2) - Bought from Ornifex
Arced Sword (starts with B, gets A on +2) - Trade Flexile Sentry Soul to Straid of Olaphis
Spider's Silk (S) - Trade weapons Ornifex the Soul of the Duke's Dear Freja.
Syan's Halberd (A) - Dropped by the Knights wearing Syan's Armor(gold) and wielding halberds in Drangleic Castle
With all the different versions out there, the publisher made this quite confusing. If you have the DX9 version of the original game with the Season Pass, you can upgrade for 20$, without the Season Pass for 30$.
Scholar of the First Sin (SotFS) is basically a "complete edition" of the game. It includes the base game and all DLC. In addition to that, there will be a patch that adds things like new NPCs and re-balancing that is already included in the SotFS edition, but will be available as a patch for the original game as well.
The benefit of upgrading your DX9 to the DX11 version are improved graphics (obviously), and gameplay changes that are exclusive to the DX11, Xbox One and PS4 version. These include new placement of the enemies (e.g. Heide Knights actually being in Heide's Tower) and more online players in a single session. These changes will not exist in the DX9, Xbox 360 and PS3 versions.
The SotFS edition for DX9, Xbox 360 and PS3 is just the patched original game plus DLC, nothing more. Players of both versions will be playing on the same servers. Players of the DX11, PS4 and One versions will play on different servers, which means you can no longer play with people who have the DX9 version on PC with the new version. You will still keep the original version though.
Here is a table that details the different versions (found on videogamer.com):
Best Answer
This issue has been fixed.
Source - dated May 2015.
To note however, that while a lot of players have had issues with the Dark Souls games (especially on PC), FromSoftware have often had a very strong "Deal with it" approach to player complaints, often stating that apparently "buggy" features are working as intended; the latest being the Dark Souls 3 "poise bug".
The reason for this approach is that firstly; the game was developed to be difficult; often phrases like "frustratingly difficult" being used to describe it. After all, the tag line for the series is "Prepare to Die". Secondly; the game was actually developed by the dev team, for the dev team*. That is, they developed a game that they wanted to play. They created the features they wanted, they created the challenges they wanted. Effectively, we're actually playing somebody else's game.
*Reference needed.