Shockingly, Comcast Xfinity is ranked worst. 
More:
https://www.slashgear.com/1279169/major-internet-service-providers-us-ranked-worst-best/
I am a Spectrum customer, and I disagree that AT&T ranks higher than Spectrum. When I had AT&T DSL, the service would go down on a regular basis. When I would call in to complain, the reps would blame my equipment. Spectrum cable has been rock steady. Also, for me, the rate is $29.99, because i have a grandfathered Time Warner plan. No data caps (so far).
Much like mobile phone service, the experience is location dependent. When I lived in New Hampshire, Comcast was my ISP. Their customer support was just as bad then as it is now but it didn’t matter because I never needed support as the service itself was rock solid.
When I moved to Florida, Comcast was the incumbent high-speed ISP. The service in my part of Florida was awful (up and down frequently). I attribute that to the fact in Florida the coax feeds are buried underground. South Florida has a very high water table as in it’s basically a filled in swamp. In NH, the infrastructure is above ground on telephone poles. So, in Florida, I was forced to seek support from Comcast and, well, we know how that goes.
Eventually, AT&T brought fiber to the neighborhood. Once settling for DSL was no longer an obstacle, I made the switch from Comcast to AT&T. Some told me I would find AT&T’s support to be as bad or worse than Comcast. I don’t doubt they were correct, however, I literally never needed to seek support from AT&T because like Comcast in NH, the service has been that solid.
The thing about quality of customer service and support is it doesn’t much matter until and unless one needs it. That’s when one finds out how good the company with which they’re doing business with is.
Interesting that WOW is not even there. I’ve had them for several years now and apart from occasional outages, they’ve been OK. I’m not surprised at Xfinity/Comcast. I used them for a while but switched because they priced themselves out of reach. Back when Consumerist.com was an active website, instead of an archive, Comcast won the Golden Poo award several years running.
As for WOW, when the promotional rate on the terminal adapter (cable modem) ran out, I bought a cheap compatible from Amazon. Activating it took all of 10 minutes, and I continue to use it to this day, saving $100+/year on rental fees. That’s over 5 years at this point. Not bad for what was a $45 box at the time of purchase. WOW even sent me a UPS return labeled shipping box for the original terminal adapter.
In fact, the last time I actually spoke to WOW support was to install the new terminal adapter. If I am having connection problems I check on DownDetector. If there is a colored blob over Southeast Michigan on the WOW map then I know it is a wide-scale problem and not just me. They keep switching between red, blue and a kind of yellowish-orange. I have yet to have a failure that did not show up on the map.