All distros use the same "Linux" kernel, however all distros make slight changes to it in order make the kernel work best for them, however these changes will almost always get uploaded back to the top where Linus will merge them himself. So all use the Linux kernel, however they all have a few different lines of code in them to make them work best for that distro. It is also worth noting that distros will ship with the version of the kernel that they see fit for each version. Some distros choose a newer kernel then others. The main pro of a new kernel are improvements in driver's and hardware compatibility. The con is a loss in stability as all new code has bugs in it. So you trade features for stability. This is why distros known for being more stable will usually always ship an older kernel than the more risky distros. To find what kernel you are running enter:

uname -r

This will show you what you are running in the version of Ubuntu you have on your computer currently. Hope you enjoy!