HTML5, hands down. As of 2011, Apple rescinded support of the flash video format on all of their mobile devices. That means flash video will not work on iPhone, iPad, and anything with the iOS operating system. Honestly, there really is no reason not to serve video in HTML5 format anymore. All that is required is the conversion of the .SWF file extension to the three main different video codecs: .OGV (Ogg Vorbis), WebM, and .MP4, and using the video tag with three nested source tags pointing to the location of the three video files. There are several decent video conversion tools out there which will allow you to upload the original .SWF file and send you the converted .webm, .ogv, and .mp4 files in your email. ZAMZAR conversion tool comes to mind. Best regards.