The first active card of Dead Eye is available immediately after joining the session, the remaining 3 cards to the set are unlocked successively for reaching the level: 10, 20 and 40. Below, in brackets are the levels at which we unlock them.

Let's start with Dead Eye. When it's active a card:

• A Moment to Recuperate (2) - allows to slowly recover your health but taking any damage will stop Dead Eye ability.
  
• Paint it Black (2) - allows to mark several enemies. Pressing the trigger will automatically shoot to all marked targets. IMPORTANT! You can't hit person with active "Slippery Bastard".
  
• Focus Fire (2) - allows you and your allies to deal slightly more damage.
  
• Slow and Steady (24) - cause that you'll receive slightly less damage and a headshot won't kill you immediately.
  
• Quite an Inspiration (44) - allows you and your allies to slowly recover health.
  
• Slippery Bastard (50) - decreases the accuracy of your opponents and yours.

I think that only the Paint it Black card is noteworthy. Let's assume that we are doing a Bounty Hunter and we must quickly get rid of guard of the target. All you need to do is to activate Dead Eye, mark all the enemies and press the trigger - job will be done by the card. It also works on players.
Other cards don't give a significant advantage, which is why it's not worth to spend money on them.

Combat abilities facilitate duels with NPCs and players.

• Gunslinger’s Choice - using two ranged weapons (2 revolvers or pistols) simultaneously deals slightly more damage. Your accuracy is also improved.
  
• Sharpshooter - using a zoom deals much more damage while you take much less damage.
  
• Horseman (10) - deals slightly more damage while sitting on a horse.
  
• Necessity Breeds - when you are close to death, you deal slightly more damage. The less health you have, the more damage you deal.
  
• Landon’s Patience (18) - the more time passes since the last shot, the more damage you deal - for example, aiming for 3 seconds will deal 100 damage, while aiming for 7 seconds you will deal 130 damage.
  
• The Short Game (38) - the closer your target is, the more damage you deal. At the same time the farther away your opponent is, the less damage you deal to him.
  
• Hangman (42) - the lasso strangles the opponents, dealing minor damage to them every second.
  
• Winning Streak (48) - each subsequent shot to the same target deals slightly more damage since the last hit.

From all of mentioned cards I can recommend 2 of them: Gunslinger’s Choice and Winning Streak. The first of them is aimed at gunslingers who like to fight at close range. The second card allows to kill the enemy quicker by shooting at the body - for example, the NPC dies to 3 bodyshots by the Evans Repeater rifle at the medium range. With this card, you only need to fire 2 accurate shots.

Recovery is another skill category. It regenerate a small amount of Health, Stamina or Dead Eye.

• Come Back Stronger (10) - health regenerates faster and it begins a bit quicker after taking damage.
  
• Live for the Fight () - over the time you are slowly recovering Dead Eye.
  
• Kick in the Butt () - taking a damage regenerate you a small amount of Dead Eye
  
• Ride Like the Wind () - every time you deal or take a damage, your horse receives a small amount of health or stamina
  
• Iron Lung () - stamina regenerates faster and the taken damage is slightly lower, depending on its intensity
  
• Peak Condition (14) - sprint costs less stamina and the damage dealt is slightly higher, depending on its level
  
• Eye for an Eye (28) - killing an enemy with a headshot restores a small amount of Dead Eye
  
• The Gift of Focus (30) - stimulants, medicines and abilities that restore Dead Eye last a bit longer.
  
• Strange Medicine (32) - recovers a significant amount of health when you deal damage but health regenerates more slowly
  
• Cold Blooded (36) - killing an enemy regain you a small amount of health over the next 3 seconds

I'm still wondering which card I should recommend. I use Strange Medicine myself, it is also worth to use an Eye for an Eye.

A passive ability that can slightly reduce taken damage or even save your life in various situations.

• Fool Me Once () - you get slightly less damage with each subsequent shot you receive.
  
• Friends for Life () - when you ride a horse, you and your stallion take slightly less damage
  
• Strength in Numbers () - for each nearby ally you take slightly less damage.
  
• Hunker Down (20) - you take slightly less damage when you're hidden behind cover.
  
• To Fight Another Day (22) - you take slightly less damage from bullets while sprinting
  
• The Unblinking Eye (26) - Dead Eye and Eagle Eye wear more slowly.
  
• Take the Pain Away (34) - when you revive someone, you and that person take slightly less damage over the next 8 seconds.
  
• Of Single Purpose (40) - if you don't have a weapon or you use a melee weapon, you get a slight damage reduction from bullets.
  
• Never without One (46) - your hat will block one headshot. When you wear a hat, you take slightly less damage, but if you don't wear it, you get increased damage.

It's hard to recommend any of above cards. Never without One has most interesting ability which can save us from one-shot death.

The most recommended cards can be found in Recovery tab. Choice is very personal and depends on the player's preferences but the best of them are:

• Strange Medicine [Health]
  
• Cold Blooded [Health]
  
• Eye for an Eye [Dead Eye]
  
• Live for the Fight [Dead Eye]

I recommend to use Strange Medicine + one of Dead Eye regenerative card.
In Defense category we won't find any cards worthy of attention. Never without One is an interesting perk, but automatically we get rid of one of the regenerative card that is much more useful. Let's move on to the recommended sets:

• Offensive set:
  Paint it Black - Gunslinger’s Choice - Winning Streak - Strange Medicine
  The offensive set offers one Dead Eye card, two Combat cards, slightly increasing damage and one health regenerative while dealing damage.
  
  
• Balanced set:
  Paint it Black - Winning Streak - Eye for an Eye - Strange Medicine
  The balanced set offers one Dead Eye card, one Combat card that increases dealt damage to one target, and two regenerative ones for Dead Eye and health while dealing damage.
  
  
• Defensive set:
  Paint it Black - Winning Streak - Live for the Fight - Strange Medicine
  The Defensive set offers one Dead Eye card, 1 Combat and 2 Recovery cards for health while dealing damage and self-regenerating Dead Eye.

Paint it Black appeared in each set. It's the best and the only card worthy of attention for Dead Eye ability.



This is how my current set of cards looks like, but how does yours look? Let me know in the comments! ;]

• [RDR2] Red Dead Online – ability cards and sets
  
• [RDR2] How to enable autopilot in Red Dead Online
  
• [RDR2] How to buy a large amount of items in Red Dead Online (no processing transaction).
  
• [RDO] How to buy a large amount of items in Red Dead Online (no processing transaction).
  
• [RDO] How to enable autopilot in Red Dead Online
  
• [RDR2] "Gold Rush" ACHIEVEMENT

Own elaboration.