This is the Internet SIG so we will not get into this too much, that said an antenna is an integral part of “Cutting the Cord”.
Antenna come in all shapes, sizes and prices. If you still have the old antenna on the roof give that a try. It may work as good as anything else. If you don’t have one you can buy almost any external omnidirectional antenna, it should work great. The reason we want omnidirectional (all directs equally) is Louisville has TV transmitters in both “Floyds Knobs Indiana”, Northwest of us and transmitters in the in the hills know as “The Knobs” South of us. Directional antenna are not advised in most circumstances.
If you do not have an antenna outside or you live in an apartment like I do you could give your old rabbit-ears a try. This may or may not work well but what do you have to loose.
As for choosing one a new antenna, it has been my experience that nearly all of the antenna at Radioshack and department stores suck about the same so get a cheap one. As for good indoor antenna the Robert Heron of Tekzilla has some good suggestions…