id go with and similar to other comps that get run, depending on the prize at the time.
be it one open to australians only, or one for the overseas people only.
open to all except certain countries with silly import laws and atxes & so on.
or even explain why you should win in a 30second video or something similar or way out there kind of way
one comp i saw recently over on yt, used a script called youtube comment grabber or something similar to that, that picked a random comment
had rules like poster must have only 1 comment etc, but if one was to be run by eevblog on yt, this would be a good way to do it, rather than using something like random.org etc