The Holiday Special was shot on NTSC video (480i), so no HD unless somebody upscales the best copy. The Ewok movies were released only on DVD in modified form, and because they’re not canon anymore, I highly doubt Disney will invest in a new HD transfer of movies they pretend never existed.
Best quality? Holiday Special - the TV master or the Zion Hybrid - hard to decide.
Ewok movies were officially released on DVD (again - modified), the original versions are not available at all.