I don't think it really matters, either could work. Film would be a little better for capturing the powers and scope of Simon's abilities, but shows have more time to dedicate to character development.
But for what it's worth didn't they already officially announce that work has begun on a Wonder Man D+ show? I dunno if we'll see him before that comes out, though I suppose a pre-powers cameo in a movie somewhere wouldn't be unreasonable.