Most Helpful Guy
It depends. Do you want it to just be something for you (and your partner) to see? Or somewhere for others to see as well?
Regardless of your answer for the above question, I strongly suggest NOT getting it on you wrist. There are a lot of professional businesses that won't hire you if you have exposed tattoos. Also, I think it looks trashy when people have exposed tattoos. Like, if I go to a restaurant, and my server has a tattoo on her arm or wrist, I immediately get the impression that she just doesn't care that much about her body or her appearance.
I also think the ankle is cliché. Too many girls put too many things on their ankles that it's just not cute anymore.
in my opinion, that phrase would look good on the lower part of the top of your cleavage over your heart. It can be concealed when you enter a professional setting, but it can be exposed when you're casually out in public, and it's over your heart which shows everyone that it means something to you.
Most Helpful Girl
It's got a heartbeat in it, so the wrist would Make more sense since that's where you can feel a pulse.