Totally agree that this is so subjective.
A month or so ago, I found myself surprised to find that when I ate a Bacon side by side with a Hass, I slightly preferred the Bacon. Of course, Bacon's season was about prime then while Hass's prime taste will not come for a couple more months (in my yard in San Diego County). And I find Hass to taste awesome at the right time, as good as any other avocado I know.
I sometimes think Fuerte is my favorite, but it's not perfect. Sometimes it has a few fibers, the seed is on the large side, and sometimes the seed coat doesn't adhere to the seed. But dang it tastes so rich just to the right level for me.
Reed is hard to beat in almost every category. And the productivity blows most varieties away.
If you're just thinking of flavor, you might say Jan Boyce, for example. But it's not perfect as it doesn't peel as well as Hass does.
And how about Pinkerton?! Tastes great to me, plus its seed is tiny so you get so much flesh.
About when to harvest Gwen: it might help to refer to the release dates that the Cal. Dept. of Food and Ag. issues for commercial farmers. URL:
http://www.californiaavocadogrowers.com/sites/default/files/documents/Avocado-Maturity-Release-2017-2018.pdfFor Gwen, smalls can be picked starting April 3. I find it helpful to compare the release dates to other varieties I have. So, you might compare the Gwen release date to Hass (Jan. 16) or Lamb (July 17) just to give you the idea that Gwen is predicted to be mature some three months after Hass but three months before Lamb. It's just a prediction on their part, but I think it's useful all the same.