well atleast the term "sound quality" is better understandable than "tinny" LoL
ok, let me be more specific..
as compared to Sony, the distortion and noise levels in pioneer at peak volumes is quite high, esp with frequencies lower than 100Hz and higher than 10Khz and volumes over 80bd. this becomes quite evident when the player is rigged with a wide frequency range speaker set(which must include a seperate low range, mid range and hi range)
this observation was suggested by ELEGANT car decorators in Lajpat Nagar, and was tried and tested by CARPLUS, East Delhi.
Sony systems has better compatiablity with other brands but the product finish in case of SONY has gone down, their new variants look straight from startrek. with "plastic" looking front panel.
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apart from it, it's a total personal feel. frankly, even i would be confused to make the decision if i had to shell out the money.
whatever you decide, make sure it has a genuine warranty. a lens replacement may cost 5k.
recomended reading:
http://www.faqs.org/faqs/car-audio/part1/