+1 on the 2.4Ghz system. No interference with other radios, your rx will simply not listen to another tx.
The 'line of sight' is a myth. 2.4 Ghz does not have the the ability to go through walls and other objects
as well as the long wave (AM or FM) systems, but you will not get you rc car out of range under normal conditions.
Nothing wrong with using an older radio, but if you are in the market for a new one, 2.4 is the way to go.