what do you consider "good channels"? an antenna will only get over the air channels and not any cable channels. how many and what channels an antenna can get depends on your area. in my city i get about 32 channels with my antenna. but your city may have more or less depending.
the most important thing is how good the antenna is. they are rated by how many miles away the source can be to get the channel. if there is one missing you know you should get, look and see where it broadcasts from and be sure your antenna is rated for whatever distance it is from you. i have one rated for 60 miles and miss nothing in my area. but rural areas or larger cities may need an even stronger one to get all that may be out there. rural areas are real...