Who, and how to write when withdrawing a submission before notification? I have recently submitted a paper to a top notch conference. Only then, I have realized that another good conference has announced a call for papers recently.

My problem is that the notification deadline for the first conference is after the submission deadline of the second one. Given the chances of acceptance, my best course would be to withdraw the submitted paper, and then submit it to the second conference. However, I do not want to just withdraw the paper. I would rather send an email to the committee, stating the reason, and apologizing for the inconvenience.

My question is, which committee (among general co-chairs, technical co-chairs, advisory committee, steering committee etc.) should I send the email, and roughly what should I write so that this situation gets less cringey for everyone?
You should contact the conference editor to withdraw/retract your paper.  They may not allow you to withdraw or retract without a valid research issue.

THINK LONG AND HARD BEFORE DOING THIS

Withdrawing or retracting a paper from a conference is usually done because of unethical or incompetent research practices.  Before withdrawing your paper, consider how this may hurt your academic career.

1) You may not be allowed to publish in the original conference again.  Many people will see the withdrawal as an indication of poor research acumen.  Your actual reason, to apply to a different conference, isn't much better.  The first conference has spent time and money finding peer reviewers and such.  You just wasted their time.

2) People may not believe you withdrew just to re-submit elsewhere.  A withdrawal is a big deal.  If this comes to light later on, you will likely get some very pointed questions about what "really happened," and the interviewer will not be pleased with this answer.

3) Others may choose not to work with you if they are concerned you'll withdraw and re-submit elsewhere, pulling their reputation down with yours.  Academia is smaller than you may think.  I would personally be very hesitant to work with someone I knew would attempt to do this, as I could get me black-balled by a conference as well.