Kang has a few multiversal feats under his belt, that is, not using outside artifacts. Even at conventional warfare he's a force to be reckoned not to even talk about the potential of his time-manipulation...
However, I consider Doom to be the best prepper overall, he has shown more creativity, more willingness to go all out and more variety when it comes to resources -he's a magician after all-. Kang in the other hand is a better manipulator. The problem here is that, because of his vastly superior resources, Kang has a huge advantage with short periods of prep, Doom should eventually catch up with him, but two days is not nearly enough -much less backed by a magic adept such as Loki, Doom is completely outmatched here-.