Both villains are good. An argument could be made each way, but I wouldn't call Shen a much better villain. Belos isn't a poorly-written villain, so I don't think it's fair to say Shen is "much better" than Belos. I like them both, so I don't know how to judge them.

Belos is honestly one of the best written villains I've seen in a while. His odd sense of self-righteousness mixed with nostalgia and desperation, the contrast between the lies he tells the world and the lies he tells himself, and the combination of remorse, xenophobia, and obsessiveness make him really entertaining to watch from a psychological standpoint.

I haven't seen Kung Fu Panda since I was like five, and I wasn't critically examining villains then. However, from what I've read on this wiki, he seems pretty well-written, and far more complex than he needed to be.

Both villains are good, I'm just voting to see results

Both villains are awesome.

Not sure we can compare them since they aren’t exactly the same type of villain, and they’re both well-written. I’m voting just to see results.

Belos is an awesome villain, but Lord Shen is my take.