Tezzell's right, I did like the wind pretty much first. I used the Dodge Viper Concept. Then I used the 787 to win the F090/S and it's all downhill from there!
I played GT and GT2 when they came out so you could say I've logged many many GT miles. Therefore it's not a big deal for me to sit down first thing when I begin the game and pass all of the licenses in a few hours.
This is what I did for GT3, only I took the time to get all of the golds before competing in any of the races, which took about a week. Once that was done I used the prize cars to do some of the more difficult racing first... after completing the Rally mode, which gave me a head start on a few more killer cars to use in Professional mode.
As of now, I have Professional finished, except for the Tuscan Series, 6 of the 10 endurance races, Rally mode done and most of the non-specialized Beginner and Amateur races... which puts me at 80% complete (I did the rally stuff too) and I haven't had to purchase a single car, other than to do the double memory card, purchase prize cars from long series races thing.
I figure I'll be finshed with the game tonight or tomorrow since all of the races left are the 2-5 lap kind... well, of course except for the endurances I have left.