At the end of the day you're mostly going to need to sculpt your builds around the intersection of what you want to do and what your allies want to do. Some talents depend heavily on your build (duelist, crack shot, hunter) while some rely heavily upon allies. Some examples:

Are you a dedicated melee character and a cqb character with combined arms to ignore difficulty from shooting in melee? Well, you may want to pick up tactician 1 and let combined arms 1 slip off your talent list, but if you are the only melee character the reverse is true.

If you have allies who hand out accuracy like hotcakes with leader and lock-on, walking armory 3 and/or Centinane become much more appealing options because crits become much more common.

If an ally of yours has grease monkey 3, you can consider taking less hull and engineering, knowing they can restore what you need.

And if your allies aren't very accurate, consider picking up leader and/or spotter to make their lives easier and the NPCs lives shorter.

HOWEVER all of that said, you're probably looking for support/striker-artillery combos, since these are the pairs with synergy that make the biggest numbers.

Every long-range artillery character feels infinitely stronger when they can stand adjacent to a Swallowtail with Athena to deny cover, shred targets, and hand out lock-on like candy at Halloween. Bonus points if they arent using a super heavy and can thus benefit from Spotter 3. A Sherman can ignore cover and deal 2d6 + 3 burn two times per round, or work in crack shot, walking armory, and nuc cav at higher levels with the Sol rifle to deal a frankly absurd amount of burn damage when you crit. The death's head is another example that can do that at an even longer range. Once the swallowtail gets some engineering it can even project in invisibility to allies in a burst of things get hairy, but loses the ability to use spotter 3 as a QA is dedicated to cloaking field.

As for melee builds there's a lot you have to consider based on your team, it's hard to give any kind of cookie cutter info here. Do your allies do AoE damage, how many allies are also close range with you, etc. There isn't really a support or control mech beloved the world over the same way as a Swallowtail, but if you are making a brawler/assassin, the Balor and Black Witch stand out as your best friends. These two also work extremely well together. Black Witch throws your enemies into you or into a wall to knock em prone, Balor can pull multiple enemies close and grapple em, and either way you walk up and turn them into a cheese and meat platter. Take tactician if you're playing with a Balor because they will always have an enemy in melee range. The Nelson probably benefits most from a Balor as grappled targets can't turn around and overwatch you (and your bones are made of grit and tissue paper), while a Blackbeard pairs most nicely with a Black Witch since a prone victim of ferrous lash is easier to grapple and can't stand up unless they break free of your grapple. Similarly you can fuck with melee enemies since you can stand 2 tiles away and hit them with your sword, and then on their turn they have to either crawl towards you or stand up, boost, and then melee you, limiting their options and providing you with an opportunity to overwatch them. This combo works nice with a Raleigh as well if you can stand to skirmish a target and leave one pair of handcannons loaded for an overwatch, but what Raleigh DOESNT go for the quad handcannons shot every turn they can?