My son-in-law was over for Christmas, and he didn't know that I had an Echo dot, so to show it off I said, "Alexa, tell me a joke". It told us a lame joke. My SIL had to whip out his android phone and say, "Hey Google, tell me a joke!" and it told us a lame, funny joke. Score one for Google.

Then he said, "Google, tell me a Christmas joke" and it told us a pretty poor Christmas joke. I then asked Alexa for a Christmas joke, and it told us a funny Christmas joke!

So, clearly, in by far the most import imaginable use case, they're pretty much tied :-)