What's the difference between two distro's kernels? Ubuntu uses 3.2.0-29, openSUSE uses 3.5.x, Debian uses x.x.x... Is there a major difference? Does this make a distro better then other, I mean, a "newer" kernel(which I think it is)?
You can find a summary of the differences introduced in each new kernel here.
In general, newer kernel versions add more features and fix bugs, but the differences for the end user between minor versions are unlikely to be noticeable, unless support was added for a specific piece of hardware you use.
A new minor version of the kernel is released every 2-3 months, and given the wide variety of hardware supported the majority of changes made to each version probably do not affect your specific configuration.
In common with other distributions, the kernel shipped with Ubuntu is slightly modified from the "mainline" version, see https://wiki.ubuntu.com/Kernel/FAQ/UbuntuDelta if you're interested in the gory details.
Note that Ubuntu 12.10 Quantal uses kernel version