A head unit is the brain of your sound system. Most people call it their stereo. If you try to save money and get the wrong one here, you may not be able to expand your system very far. For example, if you do not have any RCA outputs, you will not be able to attach amplifiers, more speakers, or sub woofers.
Here quality is better than quantity. Basically you do not need to go for the head unit that ‘claims’ to have the most power. A head unit may have lots of power, but may not produce good quality sound, and may be very difficult to use.
When buying a head unit look out for:
RCA’s outputs, does it have sub outputs, does it have front and rear speaker outputs?
RMS wattage, if you are not planning to use an amplifier, you will need a higher RMS wattage, as this is the power your head unit can actually handle.
Ipod capability; often CD's will skip when there is a lot of bass, but an Ipod wont.
Ipod capability, if you plan to attach you ipod, you don’t want to buy an extra kit at an extra cost!
Also it is handy to have a head unit that can play mp3’s, so that you can eliminate having stacks of CD ’s and put them all onto one disk. Alternatively, get a player that can read DVD’s and store a very large amount of tracks onto one disk.
Make sure the front of the head unit is removable to prevent theft.
Problems with your head unit?
If you need help removing your head unit or installing the new one, have a look here!