You basically always want to pick Discovery or Expansion as a first pick. The two main exceptions I can think of are Supremacy for an early rush, Prosperity for Clone Army, and Mercantile for Merchant spam build. Personally, I tend to go Expansion -> Discovery, or sometimes only one of the two and moving on to a different tree second. Either way, both of these traditions are quite good, although they both fall off as the game goes on.
Prosperity is probably the best tradition right now. 13% specialist output is amazing. Basically, as soon as you don't need to grab a different pick, you should be picking up prosperity.
Diplomacy is basically only picked to get a federation, although 2 extra envoys and free favors are also useful if you plan on playing the diplomacy game. If you want to be friendly or play the GC, go diplomacy. If not, skip it.
Supremacy is still the fleet civic, so whenever you end up about to go to war (or already in a war) supremacy is good. Still, it doesn't provide any benefits unless you are already at war/have a large fleet, so only get it right before war. Even for a peaceful game I'll grab supremacy before the end though, to fight off FE/AEs and the Crisis.
Domination and Harmony kinda fall into the same sorta niche for me. Kinda meh, will maybe pick one up towards the end. Generally one if not both of these end up not making the cut. Synchronicity (which is basically harmony) is a fair bit better, at least for hive minds, since the 2 amenities from synapse drones really helps.
Adaptability is interesting. +10% habitability and the building slot are very good, and the reduced housing is nice as well. I generally pick this second for doomsday, since the habitability effects your homeworld and stacking reduced resettlement, nomadic trait, and evacuation protocols civic lets you get free resettlement. There is also the fact that stacking adaptability, unyielding, and a planetary shield gets you to -100% bombardment damage, meaning your planets can't be bombarded at all.
Mercantile I think most people in this thread are mis-rating. Yes, if you are going for the void dweller merchant guilds functional architecture spam merchants build, of course the tradition is going to be amazing. If you aren't doing that, then it's not that good. Still probably worth being picked, but getting the trade policy isn't necessary by any means.
Unyielding I think is chronically underrated. Relying on starbases as a deterrent/protection while tech rushing is commonly done, and so if I was going full tech rush I'd probably grab this after discovery and prosperity. For an empire going full war aggression unyielding is also good, since the -50% starbase upgrade cost will result in a savings of tens of thousands of alloys. And finally there is the combo with adaptability for 100% bombardment damage reduction, meaning you can have practically unbreakable fortress worlds.
Subterfuge is just horrible. Even if espionage was good, it would still be bad. The only time I'd ever pick this tradition would be for an RP espionage build, and even then I'd probably go diplomacy first since the extra envoys will be more useful.
Finally, Versatility. Generally, this tradition is just kinda meh. Nothing is bad(well, besides the finisher), but all together it just falls a little short. If I do end up with space for this tradition, it's last.