Best xenos army to build, paint and play

I have a Custodes army, but I’d like to build a Xenos army too for variation. One week I like Necrons, another its Orks and another its Tyranids.

Can’t decide. Help me. I also don’t particularly want a swarm list, because I don’t have space for a million models.

Rule of cool isn’t helping either because they are all cool.

1. Which should I choose?

2. Why?

3. Give me a good 2k list to start with (not too swarmy but still good).