I was a comcast / xfinity customer for a few years. They were Meh.
Support was not very helpful unless you knew what they needed to do.
They technically have data caps but they are "suspended" for the time being - at least in KC area / Chicago Area (The two places I've had comcast)
Speeds were ok - but you could tell when school got out at 3:30 and those neighborhood teens got their gaming on.
I was never happy with them overall and I had to call all the time to get random charges /or keep my rate plan.
ALL THAT Said...
I moved to an area with Suddenlink - and they are worse - they do enforce datacap - I have 350GB @50mbps down for $39 / mo ( Suppose to be $49 but there is a special I got) - Last month we used almost 700GB so i'm sure i'm going to need to pay more
Missing comcast