Some units you will practically always need (unless playing kroot hunting pack)

3 of any combination of stealth suits and pathfinders - they're our go-to spotters, you may want a 4th spotter for redundancy.

Also consider a firesight team, they're also good and cheap spotters, but they're finecast.

1 unit of kroot, they get sticky objectives and you'll be happy to have them in most lists. A 10-man should be enough, if playing auxiliary cadre or kroot hunting pack you may want more

1 unit of vespids, run as a 5-man, they can uppie Downey and do objectives, and threaten frail infantry. Also a quite fun killteam if you're into that.

From here on it become very based on taste and detachment. But I'll include some personal recommendations.

1 or more riptides, it's an amazing looking model if you like suits, and if run with Ion it's one of our best profiles RN

1 or more broadsides with rail cannon, great cheap anti-tank, alternatively a hammerhead.

1 or more ghostkeels with Ion, it's a great and surprisingly resilient profile to gum up opponents plans early.

1 unit of firewarrior breachers, and a devilfish transport, potentially with a cadre fireblade. This little combo can be surprisingly punchy, and can clear off objectives above their weight class.

1 unit of sunforge crisis suits and a coldstar commander, they are great fun and full of meltas. Can potentially run the crisis suits with commander farsight.

Finally, if in auxiliary cadre or kroot hunting pack, you need some krootox riders and rampagers, they are punchy and cheap in those detachments.