I understand what the OP means (In some cases comes down to the template what is used)
1 - Does the video look great during the editing stage?
2 - After rending the video does it look great?
3 - After uploading it to YouTube it doesn't look as good?
Do you control/T and stretch the video size during editing? aka fill the screen.
Do you have the below screen shot (custom settings) with the your template (this will help a lot)