Formal:
* You have exquisite eyes.
* Your eyes are stunningly beautiful.
* The beauty of your eyes is captivating.
* Your eyes are a work of art.
Informal:
* You have gorgeous eyes.
* Your eyes are beautiful.
* Wow, your eyes are amazing!
* I love your eyes!
Romantic:
* Your eyes are like stars.
* I could get lost in your eyes.
* Your eyes are so mesmerizing.
* I feel like I'm looking into your soul when I look at your eyes.
Descriptive:
* Your eyes are sparkling like diamonds.
* Your eyes are deep and mysterious.
* Your eyes are a beautiful shade of [color].
* Your eyes have a captivating gaze.
You can also use metaphors to describe the beauty of someone's eyes, such as:
* Your eyes are like pools of water.
* Your eyes are like windows to your soul.
* Your eyes are like the sun shining brightly.
The best way to say "have beautiful eyes" depends on the specific situation and your relationship with the person you are speaking to.