I ended up getting six shakes in all from the major fast food restaurants near me (in a single afternoon no less; don't worry I didn't finish any of them, but I did bring people to reduce wastage).
Here's how it all shook out (ranked from last to first):
6. Burger King (shown above)
Price - $2.49 for a 12-oz small
Burger King's Chocolate Shake was way too sweet and syrupy, but fairly thick. The whipped topping was weirdly waxy.
5. McDonald's
McDonald's Chocolate Shake was just a little less syrupy and sweet than Burger King's version. It was fairly runny but that also makes it easier to drink. It comes with whipped cream and a cherry.
4. Arby's
Arby's Chocolate Shake had an interesting flavor with a good amount of depth to it, but didn't quite taste like chocolate to me. It was thick but also notably icy.
3. Carl's Jr.
Carl's Jr.'s Chocolate Shake was not well mixed; there were solid chunks of vanilla ice cream (along with Jack in the Box, Carl's Jr. shake was made with ice cream rather than soft serve). I've had shakes from Carl's before and never had this problem, so I'd chalk it up to operator error.
It was very thick and somewhat hard to drink. There's a good level of sweetness and chocolate flavor to it with just a slightly bittersweet note. They didn't skimp on the ice cream. This one felt the most like something you'd make at home.
2. Jack in the Box
Jack in the Box's Chocolate Shake was just a little syrupy, but still very good. It was very chocolaty with some nice dark notes. It comes dressed with whipped topping and a cherry
It had a thick, uniform texture that was just right.
1. Wendy's
Wendy's Frosty is technically not a shake but was my favorite of the bunch (if you want to go by that technicality, that would make Jack in the Box's shake the best of the ones I tried) and still quite creamy. It delivered a smooth, mild, milk chocolate flavor with a bit of vanilla to it.
There's an icy, almost frothy quality to it that's really enjoyable. It's really like eating a light, frozen cup of chocolate milk. It was also the cheapest of the bunch, which is a bonus.
As to why Wendy's was better than the rest, I would chalk it up to the fact that none of the chains bother to use chocolate ice cream to make their shakes (the ones that do use ice cream use vanilla since it works as a base for other flavors). And while Wendy's doesn't either, they benefit from Frosties being tumbled in the machine rather than blended to order with syrup.
