This question/comparison just kind of hit me tonight. While I've know both songs for decades, studio and live, I've never quite thought they were so close in comparison or connection. I was walking my pup tonight, and was listening to Dreamer Deceiver. The song structure similarities to Child in Time all of the sudden fell into place. I think instrumentally Child in Time is a bit more complex, but vocally? While I'm sure for most folks Child in Time is more popular and well known, I would hope you will give both songs an equal un-objective listen before coming to a decision. So...take a moment...listen to both track comparatively.
For me? I'm not sure which reigns supreme. That being said, I think they are very close....probably more close than some would think. Especially if you include multiple live versions.
Child in Time - Deep Purple
https://www.youtube.com/watch?v=PfAWReBmxEsJudas Priest - Dreamer Deceiver
https://www.youtube.com/watch?v=GjMizl3qQGE