I voted for lemon polenta. If I were at a party and all of the choices were available, that’s the one I would eat. Also, most people like lemon, and the fact that you can make them in advance is a big advantage for a party.
I use peanut butter and Karo syrup .
I thought they were cone-shaped. It’s right there in the name —
‘s cone
The ones I’ve had varied, but most of them were triangular.
All the options looked good to me. I have noticed that on a table full of various dessert treats the brownies most consistently are eaten up. YMMV. Not always against a particularly attractive looking and tasting alternative, but more often than most other offerings. Perhaps people expect brownies to always be good enough, or taste as expected without surprises. Sometimes unexciting and dull helps people make a choice, but I definitely prefer to see alternatives.
Anyway, if you were providing the only option then brownies are a safe bet, although too sugary or chocolatey for some maybe. I think all the choices are good though and would be happy to try any of them.
The ones I make are round and blobby. But triangular is a popular shape, too.
The woman who brought the other cookies just asked me for the recipe. 
So that’s a win.