The most romantic or pleasing phrase anyone could use would be 'you look beautiful'.
This works all the time when you use it in someone's native language.
If you're travelling to Rajasthan or giving your best shot to a Marwari (you know what I mean), this could help you a lot.
This also is said in 2 ways.
One being respectful and the other being informal.
You look very beautiful/handsome
Translation
Respectful
To tell him: Aap ghana futra dikho
To tell her: Aap ghani futri dikho
Informal
To tell him: Tu ghano futro dikhe
To tell her: Tu ghani futri dikhe
This works all the time when you use it in someone's native language.
If you're travelling to Rajasthan or giving your best shot to a Marwari (you know what I mean), this could help you a lot.
This also is said in 2 ways.
One being respectful and the other being informal.
You look very beautiful/handsome
Translation
Respectful
To tell him: Aap ghana futra dikho
To tell her: Aap ghani futri dikho
Informal
To tell him: Tu ghano futro dikhe
To tell her: Tu ghani futri dikhe