Ubuntu always is more stable than fedora, also because fedora is a test distribution for redhat
Yes, because Ubuntu is known for being such a stable distribution and is not taken every 6 months from Debian Unstable and claim to do in that time what takes two and a half years to Debian developers. And because they don't dare to enable ridiculous things like PulseAudio or Desktop effects by default. Also, they normally take the right decisions on behalf of their users.
Fedora, vs UBUNTU released versions are essentially the same. Only Fedora is snappier, and between 6mo and a year ahead of UBUNTU for the same applications.
I suppose it's very easy to see the 6 months difference right now due to KMS. F11 will have KMS for 90% of graphics cards out there (Radeon R600+ and Nvidia will be disabled by default, though), and Ubuntu will have nothing