I too am in the camp that just switched from ATT Uverse to Comcast within the last 3-6 months.
The reasons were several... First of all, I was paying for ATT Uverse Internet/TV/Phone package, and the bill I was paying was $154/mo (which was their promo pricing still). The promo pricing was ending, and I calculated what the new price would be for all of this, and it was over $170/mo. My family decided it wasn't worth it, and we were 'cutting the cord' for TV.
With that price from ATT, I was getting 18/2 internet speeds (actually got about 23/1.5). They couldn't get me any faster service in my neighborhood, they tried to boost me up to their top teir in my area of 25/2, but the speed went down instead of up. Just to get the 18/2 plan, they had to bring 2 lines to my house and bond them on the side of the house. The non promo price for internet alone was going to be $65/mo.
I switched to Comcast, internet only, and was able to get a 200/10 plan for $70/mo, which isn't bad. When the deal runs out, it will be $90/mo, at which point, I may keep it, or lower it down to their 100/10 plan for about the same price I'm paying now, which is still 4X faster than what I got on UVerse.
I signed up for a 3rd party VoIP provider for home phone, (Ooma in case anyone is interested), and pay about $12/mo for this, instead of the $40 that ATT wanted to charge. TV is being taken care of with streaming services, currently Hulu, but may move around as needs and content change, along with several FireTV boxes running Kodi as well.
Comcast speeds have been great, my actual speeds I'm getting are 240/12, so looking at this, the 'extra' provisioned speed I'm seeing over my advertised plan is more than entire UVerse plan speed! Couldn't believe it, and am happy at this. Plus, right after I switched, ATT announced they were going to enforce Caps, while currently Comcast has their Cap "not enforced" at the moment (for however long this lasts, but either way, staying with ATT would have gotten me Capped earlier anyway).
With Comcast, I was able to purchase my modem myself, and own it, instead of the forced monthly rental from ATT UVerse, and the service hasn't gone down in the several months I've gotten it, so it's not all bad. Granded I haven't had to deal with Customer NonSupport yet, but that's never fun no matter who your provider is. Another bonus was my "ping" time went from 32ms on UVerse to 12ms on Comcast, so it's better for gaming and other lower latency activities.
All in all, I'm saving a ton of money for way faster service. Granted some of the saving is from cutting the cord, but even taking TV out the picture, and comparing Internet/phone services, I'm still paying less for much more than I was getting before.
These are the reasons I switched, which made sense for me in my situation in my area. It sounds like different areas have different services for both Cable and ATT offerings though so it might not be the same story everywhere. It seems some areas are lucky enough to have ATT offer >100Mbps plans, which in my area they couldn't even touch. Also, even though I'm in the Bay Area, my neighborhood is an old neighborhood in the suburbs and there is no way Fiber of any kind is going to get brought in anytime while I'm alive, so I'm wasn't going to hold my breath for Google fiber or Fios.