PCI or External

This depends on a few things.

* Are you using a laptop or a desktop? Laptop = External Card or PCIMIA card. Desktop = Either one

* Do you have room for a PCI card in your case/car?

* Do you want to do all tuning via software on the computer or are you going to be tuning with an external processor (like the Alpine PXA-H701 processor for instance).

* Have you spent a decent amount of money on sound deadening your vehicle and on audio equipment for it? (greater than $1000 in most cases).

For a list of external cards see this compiled list.