Man, I love mixing time signatures, and loop lengths.
It`s nice to build a riff that loops in 4x4, but to different lengths.
say, 5 beats and repeat instead of 4.
Or 5 bars etc.

as for what time sigs I use.
any and every.
they all have different effects.
these days I just try everything I can to get something interesting going.
Mixing signatures is a nice way to introduce a semi random element into your tracks.

I do it with percussion, hats, synths all sorts.