I think I have a mix between natural and worked out. I grew up playing soccer, so that helped sculpt my legs and ass. I still workout, but I don't do exercises that directly focus on my ass. Just cardio mostly.
I think any of the 3 is fine, as long as it looks good.
I have a natural one and I've started doing yoga so hopefully it tones a bit. My BF approves, he's a bodybuilder so even his ass is super toned it's weird but I'm not into asses