What do you want your empire to do? I think you'd be better off if you decide on some kind of concept, and pick traits, ethics and civics based around that. Thinking up a species and their society is half the fun for me. Besides, it's hard to assess the optimal min-maxing in the current meta because it's all new, and the new elements interact with each other in new ways, all with a layer of potential synergies from Traditions and Ascension perks on top.
Some things I've found to work well...
If you want a lot of wars: Fanatical Purifier (requires Fanatic Xenophobe + Militarist) build that stacks ship fire rate, so get the Distinguished Admiralty civic, then finish Supremacy Traditions early. Fire rate translates almost directly to DPS, so it makes your ships individually much more powerful than other species'.
If you want explosive expansion and not having to do deal with factions: Hive Mind, civics don't matter, but get the Very Adaptable trait. This makes planets that would normally be "red", ie not settlable, just dip into yellow. Usually that wouldn't be great, as happiness would be capped at 40% - but hiveminds don't care about happiness, so you can go absolutely ham and colonize whatever you want. They'll dip into the red if they have negative hab modifiers, but you can get an additional 10% hab from the first Tradition in the Diplomacy tree, and with a couple of the 5% hab techs you can basically settle on Tomb worlds. That's not all though: Get the "Private Colony Ship" tradition from Prosperity, and you can crank out colony ships at a ridiculous rate. Their normal drawback (a higher chance of divergent ethics) doesn't apply to hive minds, so... This is extremely cheesy, but kinda fun. Probably a nerf candidate.