There is nothing as 'best' in car audio. What sounds good to your ears and has decent reviews i.e. no really strong, negative reviews, will be the best for you.
Having said that, I would advise that you first determine your budget, after doing a bit of research on the WWW. Select the 'best' components that your money can buy and get it done from a professional installer.
I am listing some good brands to consider at each component level:
Headunit
1. Pioneer - VFM
2. Alpine/Eclipse - expensive but worth the price
Component speakers
1. Illusion Audio
2. Ground Zero
3. Bull Audio
4. Hertz
5. JBL
Co-ax (6x9) speakers
1. Illusion Audio
2. JBL
4 channel Amplifier
1. Kenwood and Blaupunkt for budget range
2. JBL and Ground Zero for higher end
Subwoofer
1. Ground Zero
2. Image Dynamics