Equalizer, Which one or Not at All?

I hate to disagree with you all. But IMO an EQ is crucial only depending on what kind of music you're listening to.  Its very easy to tune in Hip Hop or Pop music because of the clean sound and production value those tunes usually have.  On the other hand I listen to Metal and Hardcore all day with shredding guitars and double bass etc.  The production quality is night and day when comparing some cd's.  I use a 12 Band Alpine unit with Sub level & Crossover control built in.  Its done great for me I love the idea of actually physically moving a slider instead of trying to press 30 buttons to get to some obscure sub-menu for the 100K adjustment etc.  That being said, most new head units have a lot of EQ control built right in.  I really like the Pioneers for sound control and I believe that most have Sub Level and frequency controls as well.

but heavens yes, If you do buy one.... stay away from the cheap stuff.... You get what you pay for!

"As a matter of fact tuning for a specific type of music seems a bit hypocritical "

What?  You don't think that different cd's of different quality and production value need to tune out excessive noise or bring up needed frequencies in order to try to obtain the "flat" sound?

An EQ is intended to be set up once and left alone.  It is to correct shortcomings or tame resonances and responce curves in your system.  Tone controls in the HU are designed for the minor adjustments sometimes necessary when listening to CDs.

Some CDs are poorly recorded and sound worse than others, yes.  But the degree of low production value you seem to imply leads me to think of bootleg or garage band recordings, not commerical recordings.

I listen to all sorts of music from death metal to rap to jazz to classical, and have never needed a full-blown EQ.  I tried one for a while and removed it as I left it set to flat.  If you need more than the tone controls on your HU to tame the rare harsh high end or weak low end as you change from CD to CD, then either your system has issues or the CDs you listen to are poor quality indeed!

But hey, to each his own and if it's working for you go for it.