Formal:
* I eagerly await your response.
* I anticipate your reply with interest.
* I would appreciate hearing from you soon.
* Please do let me know your thoughts.
* I am interested in learning more about your perspective.
Informal:
* Let me know what you think.
* Get back to me when you have a chance.
* Looking forward to your response.
* Can't wait to hear from you.
* Hit me up when you have a moment.
Other Options:
* I'm eager to hear your feedback.
* I'm curious to hear your thoughts.
* I'm interested in learning more.
The best synonym to use will depend on the context of your communication and the tone you want to convey.