Recently Comcast Xfinity started making changes to their service so you need a DTA or Digital Transport Adapter to get even the basic channels. We went along with is and installed the devices on our tvs. They get pretty much the same channels but there are a few downsides.
First, you have to use their remote control which is very basic. You won't get all the options from your normal remote control unless you use it along with the Comcast remote. Even then some features such as deleting channels you don't want will not work. Second, there are tons of blank channels you have to navigate around. And finally, the picture quality is just not very good. Not only that but this basic service costs about $20 a month.
I decided to try out the basic digital antennas to see if the results would be better. I was able to pick up a couple antennas for less than $10 each. I hooked them up and did a rescan of the channels. At first some of the channels were a bit choppy, but after a little adjusting, I got pretty much all the same channels as Comcast except the picture quality was now much better. Not to mention, the antenna service is free. So of course we are going to stay with the antenna to get the better picture and avoid paying the extra $20 a month for basic channels from Comcast.
If you just want the basic network and local channels, the antenna is the way to go. If you live near a big city, you should be able to get by with a non-powered antenna. If you are further away from the broadcast towers, you might need to get a more expensive powered antenna. Even those are only about $40 for a good one.