I had a £750 budget and the bike shop had the Z85 for £740 (£925 list, reduced as previous year) and a Giant Defy 2 for £720 (£800 list -10%). I was set on the Defy 2 until the Z85 became available at that price point.
Spec wise, the Z85 looked better to me, with 105 and carbon seat post, and looks wise the smoothed welding on the frame. However, I am not competent to say how the actual frame compares.
Warranty wise I think the Giant wins, lifetime on frame, as opposed to 2-5 years (I can't remember) on the Felt. The Giant is also lighter. Also there are far more reviews and people on these forums with Defy experiences.
I had to replace the rear hanger on the Felt, and it was no problem sourcing that part at all, the bike shop had it in stock and readily available online too. This was due to damage caused by thieves, not a fault on the bike.
In the 3 months I've had it now, not had a single problem with anything on the bike except the rear wheel hub needed a bit of oil/grease under the rubber cap to stop it squeaking. 1500 miles later I'm still on the same tubes and tyres, without any punctures at all. It is my first road bike, so nothing to compare against, but once I got used to the road bike position, I find it comfortable and fast, and have ridden 70 miles on it in my longest journey with plenty of 40-50 milers on the weekends.
If the Giant Defy 1 was the same price, I think I would have gone for that definitely though!
