I have had more JVC units than I care to remember, and have never once been let down by them. But by the same token, I have installed plenty of Pioneer units into other cars and havent heard of any real problems with them.
In terms of sound quality they will be about the same. If you intend on using the standard speakers you will never hear a difference between them.
They are both very even, so go for the one you prefer the look of and can get cheapest. Also look at accessories for them with a view to future upgrades. Both of them offer iPod control, but unfortunately neither off full-speed iPod control like Alpine do.
In terms of sound quality they will be about the same. If you intend on using the standard speakers you will never hear a difference between them.
They are both very even, so go for the one you prefer the look of and can get cheapest. Also look at accessories for them with a view to future upgrades. Both of them offer iPod control, but unfortunately neither off full-speed iPod control like Alpine do.