None... 2 are too small, 2 are too large
Can you get the person who created the titles to do so to match your project?
Or, you need to convert one of the large size files to match your project
And to add to John T's comments, if they can Export them as DV-AVI, or MOV [Animation], that will be much better than FLV, and easier to work with, than MP4.
If you had no other choice, and had to pick one of these sizes, which would you choose?
Unfortunately, that is my only option. It's very important intro titles and the black bars will be acceptable. I see that PE9 will accept the MP4, but not the FLV.
It's a lot easier to throw pixels away than to create additional ones. I'd be inclined to try the 1,280 x 720 first. If that is not good enough then 640 x 360 with black bars.
Insanity is hereditary, you get it from your children
I agree with Neale. Go large, and scale down, and probably crop (effectively crop by the Frame Size), and MP4 will just have to do.