For the sake of safety, I would probably put a PC817 optoisolator feeding the power transistor, which then optically isolates the control from the mains.. no electrical connection at all. I have a bunch of them I bottom-fed off of ebay a while back, they are a good item to have around for just this type of thing.
I'm trying to simplify this as much as possible, assembly, bulk, and cost. I figure on wiring this up and then basically potting the whole backside (everything but the power and control lines) in epoxy, so there's going to be no open conductors anywhere.
The problem with using AC directly is that you are dealing with AC, and that becomes a problem if you want to do things like strobing. High voltage DC is still DC and far more controllable. If I were simply going for a full-time illumination, doing the reverse-parallel thing would be a good choice though...