I have a Comcast business line. While I've never tested the unlimitedness of it, it does have its own sets of pros and cons:
+ Constant, consistent price. There are no promo deals of any sort.
- More expensive by $15-20 per month.
+ Cable modem is provided (they call it the Comcast Business Gateway) at no additional charge.
- They call all of the freaking time trying to upsell you on voice service. Seriously, like 6-7 times per week. I finally blocked their number from being able to dial my phone.
+ TV is "only" $5 per month more for the basic channel lineup
Just decided to check on the unlimitedness... My father's company has Comcast Business Internet and I setup their network. I think they have 15 employees, 5-6 of which would regularly be using a computer/internet connection.
The Buffalo DD-WRT router they're plugged into---Comcast gives you their own, but I wasn't trusting of a router that they likely had remote access to, so I installed an inner network---indicates that he's been doing a little over 500GB of transfer per month for the last five months. I haven't heard of any problems with him getting notices of going over (but I am going to have to ping him about those numbers... they're a manufacturing outfit and I don't think anyone there knows what a cloud service is ... most likely they're unwittingly becoming a cloud service for a botnet).