JBL or Aftermarket HU?

[SpiderVann]

I am picking up a 2004 4Runner next week and it has the JBL 6 disc HU. I play mostly mp3s and would like to upgrade this. I thought about replacing it with the 07 JBL 6 disc, but does anyone have knowledge of how the JBL HUs sound compared to aftermarket HUs like Pioneer, etc?

Any help is much appreciated.