You're all forgetting the most powerful Rookie of them all, Keramon. He can digivolve to Diaboromon in no time, and that Diaboromon can make millions of copies of himself. If I wanted to go for looks, I'd go with either Bearmon (Kumamon is a Human Hybrid, the equivalent of a Champion, believe it or not), or Armadillomon. My favorite non-Rookie is RhinoKabuterimon (Beetlemon and MetalKabuterimon's fusion evolution).
"I looked up and saw you;
I know that you saw me.
We froze but for a moment
In empathy."-Rise Against