Your need for an antenna will vary based on your proximity to the broadcast tower, strength of signal, hills, building, etc. between you and the tower.
Some tuners do a better job pulling in distant stations. Some are better at separating out signals that are close on the tuner dial. That kind of info is also on the fmtunerinfo site.
This site is helpful in seeing where you are in proximty to the broadcast tower: Coverage Maps FAQ (radio-locator.com)
If you're close, a simple di-pole indoor antenna might be fine, but a roof antenna should give you a better signal, even if you're close. I've tried some indoor antennas from Terk (not so great) and Magnum Dynalabs (decent). They may or may not be better than the free or almost free dipole antenna, depending on the station and other variables mentioned.