This Seven Knights 2 Guide provides you with a TL;DR Reroll pick, Hero Selection Ticket picks, Tier List, and Heroes ratings, gear recommendation & analysis, which will hopefully help you to decide on which heroes you may want to reroll or use your Hero Selection Ticket for. Will update the guide with more heroes as we progress.
TL;DR ReRoll Guide
The short answer is Karin!
According to many Korean Server players, Seven Knights 2 is completely a different game if you have Karin, so it’s the number 1 priority for reroll. You are able to get Karin after 7 days as a reward though.
Elena’s Sword Cosette

Since you can get Karin after 7 Days, the Legendary+ Cosette being the game’s top PVE DPS (the Global version Heroes inherits the latest KR version changes) would be what you should aim for, she would significantly speed up your Quest Line & Dungeons.
Legendary+ Shane’s DPS output with her specialized weapon may surpass Cosette, however, Shane’s melee, so she has to dodge attacks, which will most likely affect her overall output, so Cosette has our pick!
Rare Hero Selection Ticket
You’ll be given a Rare/Rare+ Hero Selection Ticket after the 1st level of Celestial Tower, you’ll also 3 additional tickets if you make any deposit into the game, we recommend the following, listed by order of priority:
For more details, please refer to this article
Tier List
The following Tier List is from the Japanese game wiki gamewith which corroborates mostly with our conclusions in this guide

Heroes Ratings, Gear & Analysis
The information below is primarily based on the excellent guide by Korean Server player SEAKMA (amy58885) along with some of our in-game research.
Ratings Definition
S – Suitable for almost all instances or situations, or must have
A – Needed for specific occasions, usable in other situations
B – Needed in few specific occasions, not worth it in others
C – Next to useless
Common
Lene

Role: Universal (Attack Type)
Rating: B
Usage: Group Battle (Pirate) / Parts of the main quest line
Analysis: I would have probably have rated her a C if not for specific occasions that requires her to be used. In Group Battles, she acts as the suppression character, however, there is a rare+ character that will replace her for that. Thus, she’s won’t be used except for some part of the main quest line or dungeons that’s compulsory for her to be used.
Lukey

Role: Ranged (Buff Type)
Rating: B
Usage: Auto Dungeons / Specific dungeons or quest lines with multiple enemies
Analysis: Even though his damage is low, his passive & ultimate buffs are quite useful, there is a rare+ character that provides similar advantages later on.
Kade

Role: Tank (Universal Type)
Rating: C
Usage: Any low level Dungeon
Analysis: Only about half of the low level dungeons and a few Group Battles need a Tank, however, other Tanks will probably be better, there is rare+ version of him.
Cheng Chen

Role: DPS (Universal Type)
Rating: C
Usage: Any low level Dungeon
Analysis: Only usable as a transitional character in the beginning, replace her with other DPS type heroes in the later stages.
Melissa

Role: Support (Healing Type)
Rating: C
Usage: Any low level Dungeon
Analysis: Even though she’s a ‘healer’, only her 3rd & ultimate skill actually heals, not useful in sustained battles, replace her with her rare+ version or Karin later in the game.
Greater
Adel

Role: Tank (Resistance Type)
Rating: A
Usage: Group Battle (Ice Emperor) / Any Dungeons with mobs with freeze abilities
Gear: Oath of the Protector (Increases Block Rate) or Oath of the Transcender (Increases All Skill Levels)
Analysis: Besides his passive Freeze Resistance, his overall abilities are quite balanced, his Nobile Barrier used along with his Ultimate can make him as tough as a legendary tank in that instant, but quite brittle without those 2 abilities, needs to dodge attacks while those abilities are on cooldown!
Black Rose

Role: DPS (Support Type)
Rating: C
Usage: Any Low Level Dungeons
Analysis: Compred to Chen Cheng, she’s obviously a single attack type hero, but her damage % is still lower, and her Ultimate’s damage is also held within a limit which greatly reduces her damage potential, can be used for low level dungeons in the beginning.
Claire

Role: Ranged (Support Type)
Rating: B
Usage: Specific Main Quest Line / Dungeon
Gear: Oath of the Assassin (Increases Crit Rate)
Analysis: She has extremely high crit. rate to begin with, coupled with her passive & skills, it can be increased above 50% which is extremely high amongst the Greater heroes.
Guilahan

Role: Universal (Resistance Type)
Rating: A~B
Usage: Group Battle (Pirate) / Any Dungeons with mobs with Burn abilities
Gear: Oath of the Transcender (Increases All Skill Levels)
Analysis: High usage in Group battles, and with more and more dungeons with fire damage, he’s almost become a must have for everyone.
Henry

Role: Ranged (Resistance Type)
Rating: B
Usage: Group Battle (Black Knight) / Any Dungeons with mobs with Paralysis abilities
Gear: Oath of the Berserker (Increases ATK) or Oath of the Transcender (Increases All Skill Levels)
Analysis: Currently the only hero with poison effect, primarily relies DOTs for damage, can be used both as DPS and Resistance in Group Battles, since poison is DOT and bypasses defense, many players use Henry in the beginning since he’s quite easy to level up. Replaced with other DPS later in the game, only seen in Group Battle (Black Knight) Dungeon nowadays.
Ian

Role: Support (Resistance Type)
Rating: A~B
Usage: Group Battle (Poison King) & (Shattered Emperor) / Any Dungeons with mobs with Poison abilities and needs multiple support heroes
Gear: Oath of the Transcender (Increases All Skill Levels)
Analysis: A good Support type hero is hard to replace, and there is more and more dungeons with poison type mobs, which makes Ian a must have these days. However, a major fault with him is that only his 3rd & Ultimate Skills heal, and the lack of any defensive skills make his survivability lacking.
Scott

Role: Universal (Resistance Type)
Rating: B
Usage: Group Battle (Shane) / Any Dungeons with mobs with Bleed abilities
Gear: Oath of the Assassin (Increases Crit Rate)
Analysis: Almost useless in the beginning, since mobs or BOSS with Bleed ability are very rare, the only BOSS with such ability was in Chapter 8 of the main quest line, and his Bleed damage was so low that most people will just ignore it, so Scott’s usage had been extremely low. Alas, with the new update that released Group Battle (Shane) has finally made Scott useful.
Tristan

Role: Tank (Universal Type)
Rating: C
Usage: Any low level dungeon
Gear: Oath of the Holy Knight (Increases DEF)
Analysis: Evan’s lower grade counterpart, pretty much useless, he inherited some of Evan’s Reflect & Recovery abilities, but he doesn’t have any defense or blocking buffs, should just use Adel instead.
Original Author: SEAKMA (amy58885)
Original Source: 【攻略】各階級英雄定位與評鑑(更新稀有+英雄與七騎士)
Translated & Edited by: NeoCloud
А где легендарный Вальдур??????