I don't know much about debian and ubuntu. I just want a good system to be very stable and with good features such as gcc4.8 etc. Ubuntu 13.10 is not stable with my testing. And debian 7.4 is seem to be too old about kernel, so it could not use much new features, especially including correct install my ATI HD 6630m driver.
So I want to learn more about debian testing and ubuntu 12.04 LTS. Then I could get a stable sys with new feature and also learn a little more about debian series sys.

12.04 is reaching end of life.

I don't Ubuntu anymore so I can't really comment on Ubuntu stability.

I run Debian testing though and there is no end of life.
Also in the Debian unstable I run there is no end of life.

I have a install that is based on Debian Sid and has been running strong for a long, long, time (years).

YMMV from mine though.

ubuntu14.04 is now available,so why not try it.And there's another choice ,opensuse is good too ,I sugest you try it .It's redhatlike system ,not debianlike .

...and is probably worse than 13.10...... Ubuntu has pretty much become Windows- gets worse with every new releaese, instead of better.

No quite yet although there seem to be a number of people who wish it would. I have it on a notebook and I guess I've been lucky, no problems so far.

https://wiki.ubuntu.com/Releases

Q: Is [insert any operating system] more stable than Ubuntu [insert any version from the last few years]?
A: Yes

Ubuntu 12.04 is equal to Debian 7 (Wheezy). Ubuntu 14.04 will be equal to Debian testing (currently Jessie). If you want a stable system with new features use Wheezy and enable backports.
Not until April 2017 it isn't. Ubuntu LTS support is for 5 years now.

I've been testing user for a couple of years and haven't had any major breakages, but indeed it has broken. A common one is fglrx, another one for example is when an application upgrades but not it's dependencies, let's say you have two packages installed: coolapp1.2.3 and coolapp-plugins1.2.3. Coolapp upgrade to 2.0.0 but the plugins package remains 1.2.3, breaking the program.

Right now I'm using LMDE as it's a more stable version of Jessie and in my opinion, Cinnamon is the best desktop environment for performance (not resources performance!)

k3lt01 mentioned enabling backports. Regards your driver issue, backports includes later kernels.

I have both Debian Wheezy (the current Stable) and Ubuntu 12.04 (also Kubuntu 12.04) installed here. Wheezy since a few months before it went to Stable, and 12.04 since 2012.

You can't get much more Stable than Debian Stable because of the way they test everything out before they release; after that you get only security updates, so you don't have to worry about updates breaking anything.

Having said that, 12.04 has been just about as solid as Wheezy here.

As has been noted in this thread, 12.04 support will continue for a few years yet. If you're gonna go with the next LTS release (14.04) and stability is your primary concern, you should be okay but you might want to wait for the first point release in a few months, in case there are a few bugs they want to get worked out after the initial release.

My Bad. Friggin Desert Scooter Tramp knows no better..

http://en.zimagez.com/zimage/desktop61.php

I run a bit of everything but am also a space case sometimes. We get good stuff down south here.

Fixed some hinky things in the above core install. It is about as hinky as Sid sometimes. Especially noeveau drivers combined with 3.14 kernel.
Fun and games on Legacy Nvidia stuff.

So I guess unstable is in the mind of your skillz.

I can't say which is "more stable"; by one definition it would be simply the one that receives less updates - regardless of how crash-prone/buggy it is; just happens that the policies are so that they try to filter out the bugs in a given release and then make it "stable"/"frozen", only add minor/security updates after that, so that it remains relatively bug-less. But it could also be that, for whatevers reason, the distro maintainers have "stabilized"/"frozen" the release in a state that would be less bug-free than the ideal. Then it would be more or less "stably unstable", in respect to the bug-affected packages.

The other definition would be "not buggy/crash-prone", but that will vary depending on the DE and applications one use, and also some degree of user "expertise" in not messing things up (less "expertise" required for that in the actual "stable"/LTS releases). I don't know if there's any official/reliable unattended bug count to compare, so the input from users will be somewhat "biased" in the sense that they will be speaking from their experience, based on the apps they use the most, that may or not be the same ones you'd prefer.

In any case, you may want to check out the apt-listbugs and dpkg-repack utilities. I guess they're available for both distros. The first one scans for bug reports before upgrades, shows the description summary if there's any known bug with the packages you're about to install or upgrade, and asks to confirm or cancel. The second one will create a "deb" package from a package you already have installed (inheriting configuration changes).

Not quite right but very close. Debian does release non-security type updates to stable but primarily as previously unknown bugs rear their ugly heads.

Very good point.

True. Thanks for that clarification.

testing is testing, stable is stable, testing is not stable, stable is not testing...

The clue is somewhere in the words themselves... it's hard to spot I must admit, took me a while as well...

A given 'buntu release is probably more stable than Debian testing. testing gets continual updates - except during freeze - so it's not a stable distribution. A stable distribution is something like Slackware, RHEL or Debian stable.