My friend have a fanatec wheel. Not sure which one (it doesn't have the orange casing but it's got the porsche wheel on it). He's been trying and trying to get responsive yet non wobbly force feedback settings on his wheel. He says that the only way some people have fixed it is to use Logitech drivers but that it didn't work for him. I base my dislike for Fanatec on my friends experiences with it.
With the proper settings, the G25 (and G27 for that matter) have a very linear and mechanical feel to the FFB response and stability. It doesn't start wobbling at high speeds and it's still right on target angle within a very short amount of time (even on high force settings).
The G25 also have versatile components for different kinds of sim-rig applications. Each individual pedal for instance is it's own component made out of sturdy metal and with pre-drilled and threaded holes they can easily be mounted on different pedal frames (if you want reverse mount pedals that is)
Negatives about the G25 or G27. The biggest downside of the G25 is the loud noise it makes, which is reduced in the G27 with the helical cut gears. Some people have also had problems with their shifters, certain gears won't engage properly. I have no experience with this problem what so ever. I guess it's a matter of bad luck. If you get a faulty shifter, maybe you can get it replaced?
Spiking and flickering in the pedals is another thing. My pedals do that occasionally. I then disassemble and reassemble the pedal which takes about one minute and it's good for another month of active driving. Keep in mind that the potentiometers of my pedals are exposed to dust since I have them reverse mounted. That might be the cause of this.
I've brutally abused my G25 for about 3-4 years (can't remember exactly when I got it but I've been playing quite actively all around this time with a couple of breaks). I've been drifting a lot with it and my drifting style isn't exactly easy on the wheel, so to speak. I've also taken apart all the components as I've done mods. I've also lubed the wheel once.
I love the FFB, versatility in the design and it does what it's supposed to do for a long time (in my case). I dislike the cable management (which I've modded to suit my liking), the loud noise which is fixed with the G27 anyways, and that's about it.
Final words, I love my G25. I think it's a great wheel. There are certain aspects that I just need which the G25 and G27 provides. I bought my G25 when there was no Fanatec around (at least I don't think). My friend seemed to like his Fanatec as he bought it so I'm sure it's a good quality wheel. However, he haven't been able to get it setup properly with FFB (not sure it's even possible) and it's just less versatile to modify to your liking from what I understand..
Would I take a Fanatec over a G27? No way, but it's up to you and what you're looking for in the wheel.