I get this question sometimes and I have been meaning to make some guides so why not start with something simple? This guide will list what skill sets recommended at this time per campaign and when you should use them

Leon: You will need two skill sets: Skill Set 1: Infinite Magnum, Magnum Mastery, Firearm 3 Skill Set 2: Infinite Magnum, Firearm 3, Breakout Skill Set 3: Magnum Mastery, Firearm 3, Shooting Wild Skill Set 4: Ak master, Firearm 3, Infinite AK Skill Set 5: Infinite mag, Grenade power up, firearm 3 Skill Set 1: Chapter 1, 2, and 5 you will use Skill Set 1. For most of Chapter 4, you will use this same skill set except at one point where you are on the plane. For all of Chapter 3, you use Skill Set 2 and for part of the plane in Chapter 4. Switch to this skill set right before you open the Valve Door in solo and in co-op the Leon partner switches before the start of chapter. You switch back to Skill Set 1 before Leon pilots the plane so you can have the firepower for the Ustanak fight. Skill set 3 can be used for the Boss fights if you have enough ammo and have good aim with it. I recommend it for Ustanak, T-Rex Simmons and Simmons boss fight with Ada. It can be used for Chapter 2 as well before the boss fight with Lepotitsa-just switch to it before the final coop prompt on the top of the Cathedral. Train Simmons does not save time in solo if you switch to it but is good to use for Coop. Skill Set 4: Use this for ch 1 and other areas of the game to skill smaller enemies quicker than with weapon switch mag. Switch to Mag for bigger/tanker enemies Skill set 5: Use this for the grenade toss in chapter 3 if needed and for the grenade toss when you have to kill all the enemies in chapter 5 ( the area before you have to run towards the camera cause if a plane falling onto the road)

Chris: Now you will need three Skill Sets: ¤(Main)Skill Set 1: Infinite Grenade Launcher, Grenade Launcher Mastery/¤Defense 3, Firearm 3 Skill Set 2: Infinite Rifle, Rifle Mastery, Firearm 3 Skill Set 3: Infinite Shotgun, Shotgun Mastery, Firearm 3

¤ Defense 3 is for you to decide if you wish to use. Grenade Launcher can be dangerous to the player(s) if you are reckless or not careful. The set up with the Mastery can do 5 bars to yourself if it is right next to you. Missing one bar and you are in dying state. For someone who isnt use to Chris' campaign, I recommend trying Defense until you learn what to do; otherwise, I recommend full damage set up...Just keep in mind of your health or it will ruin your run.

Skill Set 1: Your main set up for this campaign. You will use it all for Chapter 1, majority of chapter 2, 3,4, and most of chapter 5 up until the end. Skill Set 2: Before going into chapter 2, switch to this and use it until you beat the first Gaint. It is the most effective way to damage his weak point compared to the grenade launcher. After this fight, switch back to the Skill Set 1. Skill Set 3: Use it after you beat the final boss. Shotgun is good for destroying the barriers at the homestretch instead of waiting for Piers to walk to them and use his arm. Thanks to Wesker_Reborn for this tip

Jake: You will need 4 skill sets for this campaign (Main) Skill Set 1: Infinite Magnum, Magnum Mastery, Firearm 3 Skill Set 2: Infinite Magnum, Firearm 3, Breakout Skill Set 3: Defense 3, Jhavo Killer 2, Melee 3 (Credit to RE_Snow and RebirthXeroo) Skill Set 4: Infinite Grenade Launcher, Firearm 3, Grenade Launcher Mastery OR Grenade Launcher Mastery, Shooting Wild, Firearm 3. Skill Set 5: Infinite AK, AK Mastery, Firearm 3 (Use for the chainsaw fight)

Skill Set 1: Use this for chapter 1, and majority of chapter 4 and 5. Skill Set 2: Use for Chapter 2 and right after you use the crane to stop the elevator. Switch back to Skill Set 1 after you start the elevator with Chris/Piers Skill Set 3: Use for Chapter 3 and switch to it right when Jake tells Sherry "Sherry Now!" during the second to last Ustanak fight. You will need it for the hand-to-hand fight with Ustanak. Skill Set 4: Switch to it after the bike section and use it throughout the Helicopter fight to damage it

Ada: This campaign requires a skill set per chapter with the exception of one... so I will list the chapter right next to it instead of making a separate paragraph. Optional Skill Set: Infinite Shotgun, Shotgun Mastery, Firearm 3 (if you want to use it or have as a backup or Use it for Chapter 5) Skill Set 1: Infinite Shotgun, Firearm 3, Breakout (Chapter 1) Skill Set 2: Infinite Shotgun, Grenade Power-Up, Firearm 3 (Chapter 2) Skill Set 3: Cross Bow Mastery, Quick Reload, Firearm 3/Crossbow Mastery, Firearm 3, Shooting wild [This one is faster but the other can be used if you are not confident in using SW] (Chapter 2, switch to it right before Leon gets on the minecart) Skill Set 4: Infinite AK, AK Mastery, Firearm 3 (Chapter 3 or Chapter 5) Skill Set 5: Quick Reload, Defense 3, Grenade Power-Up (Chapter 4)