720P or 1080i

[SvennoJ]

What is the actual resolution of the tv panel?
If it's 1280x720 native, then 720p is your best option.
If it's 1366x768 you might get some more detail with 1080i. (1920x540 alternating lines) The difference will be minor anyway.

It also depends on what your tv does, de-interlacing and scaling produces extra lag. Easy to check while holding the WiiU game pad up next to the tv. 720p is probably faster.