Which is correct
Why wait until tomorrow.
Why to wait until tomorrow
Which is correct
Why wait until tomorrow.
Why to wait until tomorrow
Technically, none of them is correct. They are questions ended in a full-stop (instead of question marks).
However, matching your intention, the following is idiomatic:
Why wait until tomorrow?
The correct one is "Why wait until tomorrow". Since you have "until" in the sentence you don't need to put "to" there. You could say "Why would you wait until tomorrow?" or "Why is he waiting until tomorrow?" But not "Why to wait until tomorrow?".
Hope this helps.