Best size for mp4 video on iphones

I am publishing vertical videos from my own website, exporting them from Flash as .mov and then converting them to mp4 with Handbrake. What is the best size, width and height, for iphones? I need them to look good on all sizes of iphone screens. From what I've read, there are many factors to consider - display size, screen size in points, rendered pixels and physical pixels. But I'm hoping there is one recommended maximum size (width and height, in pixels) that covers them all. For now I'm using 720 x 1040, but need to confirm that it's OK. Thanks.