There are many variables in reasons to choose your sequence settings. How was the footage shot? What frame rate? Was it shot progressive? Frame Rate 23.976?
When shooting Progressive 23.976fps and mastering for broadcast you will need to have your sequence settings at 23.976 progressive. Then when exporting, you would then set the export for 29.97 interlaced Upper first for broadcast spec.
As a general rule, you will have a better edit if your sequence setting matches the majority of your source footage.
If your footage was shot at 29.97 progressive, then there is no need to do interlaced at all. All broadcast outlets are taking 29.97 progressive 1080 unless their spec if for something like 59.94 or other unusual needs.
IF IT IS FOR WEB ONLY, NEVER USE INTERLACED FOR ANY ASPECT OF YOUR POST.
Have a great day!