I recently posted a picture of my favorite Ferrari in GT5 - the 1976 512 Berlinetta Boxer. I have had more fun with that car than just about any other. And while it certainly can't fit every bill, it does a damn fine job at most. For everything else, there's the Ford GT LM SPEC II Test Car which is surely my second favorite car in the game. I like it so much I priced out local used Ford GTs ($300,000).
But GT6 is a altogether a different beast. I've been driving Ford GT's sister car, the 15th Anniversary Edition Ford GT40 Mark 1 to great success. And when I went to see about a Ferrari, I saw something intoxicating, which eclipsed the 512BB. And through a series of tuning, and de-tuning, its now my number one ranked most used vehicle - God I love this car. I priced it out as well ($600,000):
Ferrari GTO '84