I'm new to the series and have been playing the campaign on Easy and clicking away quite happily, but it's dawned on me that I've not picked some optimum perks for my soldiers.
Having looking through the perks I've noticed that many are complimentary, such as the Support soldiers Field Medic & Revive.
Are there other synergies like this?
TL;DR: As long as you pick skills from one side of the tree, they'll generally synergize pretty well. There's no 'optimal' perk configuration imo since it also depends highly on your play-style and strategies.
Generally, there are two skills you can pick per level, and the skills on one side of the tree synergizes better with other skills on that side. This is the same for all the classes. In your example with the medic, the left side of the tree focuses on healing while the right side focuses more on providing team support in the form of suppression fire, additional smoke grenades, combat drugs, etc.
The heavy is another great example for this, Holo targeting, Suppression, Danger Zone, and Mayhem are all on the right side and works great when taken together. However, this doesn't mean they are useless if you prefer to build a rocketeer. Some of them, such as danger zone and mayhem, also boosts rocket aoe and damage while holo targeting also affects normal attacks (personally I prefer bullet swarm since 2 attacks per round is great since you are almost always outnumbered).
There are some optimal perks from veteran players such as myself. I have learned that some builds are geared for early game battles vs. end game battles. I have used all of the perks until I got a good understanding of which one could would be better suited to survive and save the world. Here is a break down.
Heavies is the one class that I build one way, and one way only. They dominate the game with this build.
Assaults are better suited as clean up men/women. Soldiers that will either be used to take down big enemies with Rapid Fire, or walk right up and blast the last standing enemy on overwatch due to the Lightning Reflex ability.
Supports are used strictly for medical and capture purposes. With Sprinter, Deep Pockets, and all medic synergies, "support" is what the Support does best.
Snipers are great. There are two perfect sniper synergies. Mobile and Stationary. Based on experience, the Gunslinger and Damn Good Ground should switch sides on the synergy chart. Damn Good Ground is good for mobile snipers. Mobile snipers receive a -20 aim penalty (snap shot), but the other additional add-ons make up for it in the heat of battle. For example, a ambushed mobile sniper grapples to the roof of a building, and finishes off several enemies due to "Snap Shot", "Damn Good Ground", "In the Zone", along with a scope. Awesome.
Sniper “Eagle Eyes” (Scope) - Head Shot, Squad Sight, Gunslinger, Battle Scanner, Opportunist, Low Profile, Double Tap
Sniper “Mobile” (Scope) - Head Shot, Snap Shot, Damn Good Ground, Disabling Shot, Executioner, Low Profile, In the Zone
I hope this helps everyone in making optimal selections for your soldiers.
While the two sides mostly synergize internally, there are exceptions and there are significant differences between "quality" of one side over another.
For example, you can create a "mobile" sniper, who can walk then shoot with huge penalty, and shoot only targets within his/her sight range (thus exposing self to enemy retaliation) - it's really a crappy build. You'd have to be really desperate for assault units to choose this over SquadSight, which lets stationary snipers mop up everything your team spots.
An example of exception would be Heavy, where you build the heavy/assault side, and not the support/suppression side, but "Danger Zone" increasing rocket explosion radius by 2 tiles seems vastly superior to ability to carry one more grenade. Similarly, Assault has an offensive and defensive side, but Flushing shot seems like a poor trade for Rapid Fire - the +30 accuracy is offset by doubling the chance to hit at -10 penalty, shooting twice even at the reduced accuracy usually has a better chance to hit than shooting once, and once berserkers enter the field, ability to deliver massive damage quickly becomes essential.
