Beer battered onion rings, when done properly, should be crunchy on the outside, tender in the middle, and slightly sweet, as the acid has been cooked out of the vegetable. The onion itself should be hidden inside the fried batter, and the batter should neither slip off the onion at first bite, nor should it be overly thick. And when they are done correctly, onion rings can be a divine side.
The secret is in the batter. While any beer may do, I would recommend finding a microbrew that you like, preferably something local. Around here, that could be Victory Brewing, Sly Fox, Yards, Evil Genius (who, by the way, have some of the best names for their beer)…there’s just too many to list.
The other secret is making sure that the oil is hot enough, between 370-375 degrees F. If it’s too cool, it won’t cook the rings fast enough and you’ll end up with mushy rings. No es bueno.