Here's my summary of fanatec vs logitech
pedals- the clubsport pedals are the best I have ever used, but the G27 pedals are also very good, just not as good as the clubsport. The G27 pedals are much better then the ones that come with a fantec wheel though.
Feel of the wheel. The G27 wheel to me felt more like a toy trying to be a wheel then the fanatec one does. The Fanatec one feels more like an actual steering wheel out of a car to me. I really don't know why people claim they like the feel of the G27 wheel better. To each their own, but I would rather have a realistic feeling wheel then logitech wheels offer.
Adjustablity- this one is totaly to Fanatec. They blow logitech away in this category, and to me that alone makes it worth buying over the G27. There are some games that I had trouble getting the logitech wheel to feel right with, because the in-game settings didn't offer enough options. With the fanatec wheel, you can pretty much do whatever you want without even going into the games settings.
Force feedback- It's kind of a toss up for me. I liked the quick, tight response of the logitech wheel, but I also like the smoothness of the fanatec. The logitech one just felt more accurate to me, but it's also kind of twitchy at the same time. The Fanatec is stronger and much smoother, but the smoothness kind of took some of the excitement out of racing for me. If I had to choose which one was better for Force feedback, I would lean toward the G27, just because I liked the twitchy feeling a little better.
I chose the Fanatec though in the end, because of the clubsport pedals, the adjustability of settings, the ability to have firmware upgrades to add future features, and the hopefully someday addition of the clubsport shifter. I actually like the stock Fanatec shifter better the logitechs also.
I would have to give the bang for buck award to the G27 though. For 300$ it's a really good buy, but for 150$ with the 50% coupon they have been sending out it's steal.