Just got on Sling this week as an early customer as well. It takes trained eyes to tell the difference between Sling's network stream and the digital TV stream from Comcast. This is good quality of a service that is at the early adopter stage.
I decided after my weekly end-of-year reckoning about expenses that the price of Comcast, which slowly creeps up on a nearly monthly basis, isn't justified when I watch 2 channels. I decided to end my TV service with comcast within the next year. Then Sling comes along and has the two channels I happen to watch.
The downside is Sling is operated by Dish and it has all the inherent customer service problems that entails. Since Comcast is a disreputable company then this is a wash though, and on aggregate Dish service is probably equal or better. The customer service problems have been on display with their roll out, as people who were REALLY excited about the service aren't being able to get the invites for the service. The excitement for Sling has been very great, but due to the usual idiocy from the top brass (giving out bad dates for when the service was going to start) and the usual corporate idiocy of not answering legitimate questions (see @Sling on twitter).
I can't see Apple's offering to be any better. At least Sling is concerned about various platforms. I am sure Apple will force you on to their equipment, there will be no allowance for non-Mac and Android users, etc... Sony is coming out with a similar service with the same problems. I don't want to buy a PS4 when I've a Roku boxes in my house for a decade already.