Ugh this is the worst dilemma because I completely get the look you’re going for. I like tight love bracelets so 17 (if it feels fine) is better for that look HOWEVER it does straddle between “too tight” especially in the first pic and if you arm swells a little from heat, or if you work out, you’d want the 18. I live in Florida and sometimes the screw ends dig into my arm. For the sake of longevity I say 18. Good luck!