I would go with the Triode Electronics one. They had a good US maker clone the old Dynacos and added a little better filament current capability so they run cooler than vintage ones. Everyone that I know who has used one has been happy with it, and that is where I would go if I needed a new one. Heyboer makes good stuff, but sometimes they can be a bit slow to respond to inquiries. I've used thier stuff in some amps and plan to use more. I've heard Mercury Magnetics stuff and I think it sounds good, but they charge so much for their product that I can't justify spending the money on their stuff when I can get something perfectly fine for half the price or less that sounds just as good.
Greg