I've had the Echo Dot for almost a year and it's brilliant. I have external speakers plugged into it and mostly use it for news and streaming Spotify and radio broadcasts. I really don't know anything about the Google device but the Echo is a winner.
I think the thing that could be the clincher is being already hooked into Google or Amazon worlds - the Alexa can automatically buy on Amazon, and is obviously linked up to Amazon music etc. Whereas the Google one wil clinch it if you're a big user of Google calendar et al.
I have... one of each as I bought one, and won the other. Both are similar but I prefer the Google one as we ask it lots of facty-type questions and it deals with that better.
If you’re asking questions then the google mini is probably better, it also looks nicer. I was looking at the mid range google home and new amazon echo and think the amazon sounds better. I have an echo first generation and really do like it but I resort to google voice on my phone for certain questions.