.... and therefore make a short test-video - say 10 seconds - and render it with different templates and/or custom parameters to see what gives the best result is your case.
Just an example: I got a new 50 inch plasma connected to a Mac mini to play my videos - and all my former videos went a little unsharp.
So I started testing - and the soloution was to render to wmv 1360x768 instead of wmv 1366x768... ...even if the plasmas data says that its native size is 1366x768...
And as brighterside writes "there is more than size" - if you play your videos from a PC it might be convienient to see all the videos in thumbnail-view - and not all formats can be shown as thumbnails easily.