Here is the wall.

You are over thinking this. Center along with light switch and if you have kids using this make it slightly lower. IMO towel bars are a pain as no one ever takes time to properly hang towels. I’ve switched to attractive hooks in all bathrooms. No more askew towels for us.

I would probably hang it next to the light switch and leave the area above clear for hanging art, but either way will be fine. Where the studs are might sway my answer so the towel bars can be secured into a stud, if possible. eta: I may have misunderstood...is this a rack with a towel bar below? Or do you mean a towel bar? If it's a rack, it should be hung higher than that switch. Like this?

eta: where is this in relation to the vanity or shower? Is either already installed because nothing else is visible. If it's for hand towel for the vanity, I would not want to be dripping hands all that ways to grab a towel; same for the shower.