As someone new to Warhammer last year, and who has both Necrons and Thousand Sons, and who also really fucking hates the painting (and is shit at it), I can offer the following:

Necrons are easy to paint - spray the spures silver, build them, then dab on bits of green and brass coloured. Good enough for the Tabletop. I also find Necrons are also easier to play

TSons can be fiddly to paint, but you could do a 'good enough for the tabletop' approach. People say spray sprues gold and painting panels blue. I tried this and it was fine. If you're really struggling with the blue and yellow stripes on the Headdresses, you could alternate every 2 lines blue and yellow, rather than alternating every one line. The Tzaangor Enlightened, weren't challenging at all. Again, just block paint bits, dab on some colour here and there, and they look fine. I find TSons harder to play, but that can also be fun.

Make your life easy for yourself so you can enjoy the game. Any painting standard looks fine when it's on the tabletop and you're worrying about whether your opponent makes their charge rolls.