I have the 911 Turbo S Ultimate edition, and it's superb, but it was very expensive!
If you read all the reviews, their wheels are really good, the only fly in the ointment is that customer service is slow with communication problems (German company), and they aren't as slick when ordering etc, but they offer 2 years warranty, and have been creating products for sim racers for years, they trade on their quality and reputation, and do release firmware updates adding even more features to their very nice configurable LCD on-wheel menu system (Can adjust just about everything, and store 7 presets).
I will say that I was quite sceptical, and it pained me to spend so much on a wheel (No 911 Carrera wheel then), but since it's not only made it a nicer experience, but my lap times have improved quite well, the ability to dial in the wheel to me was key, as where the clubsport pedals.
The standard pedals are OK (all have a clutch), not quite as good as the Logitech G range, but their Clubsport pedals (expensive) are sublime..
If I was in the market for a wheel, and didn't care about Xbox 360 compatibility, I'd probably get the 911 Carrera, for £150 for all that, it's well enough reviewed and has all the same configurability of their expensive wheels, it's just gear driven instead of belt, which is inline with all the other wheels out there..