Git is under very active development, and both bugfixes and awesome new features are regularly added to the development version of git in a branch called 'next'. The git developers are also remarkable good at not breaking this development branch. Many people actually use this branch for their day-to-day git usage.
A downside of using this version of git is that you'll have to manually compile and install it, which is not only repetitive work, it also doesn't play nice with packaging systems like apt or yum. So why not let someone else solve that problem for you?
I have set up a continuous integration system that builds new deb and rpm source packages every day if the git maintainer has pushed new commits to git.git. These source packages are uploaded to Launchpad and openbuildservice to create packages for Debian, Ubuntu, Fedora and CentOS. It now becomes really easy to use and regularly upgrade git on your system.
Note that these packages explicitly do not use the local patches that Debian and Fedora add to git. They give you a git as vanilla as possible.
$ sudo-i # add-apt-repository ppa:dennis/git-next # apt-get update # apt-get -y install git
$ sudo-i # cd /etc/yum.repos.d # wget http://download.opensuse.org/repositories/home:/seveas:/git-next/CentOS_7/home:seveas:git-next.repo # yum -y install git
CentOS 6 is also supported, just change 7 to 6 in the wget command
$ sudo-i # echo 'deb http://download.opensuse.org/repositories/home:/seveas:/git-next/Debian_8.0/ /' >> /etc/apt/sources.list.d/git-next.list # apt-get update # apt-get install git
Debian 7.0 is also supported, again just change the url.
$ sudo-i # cd /etc/yum.repos.d # wget http://download.opensuse.org/repositories/home:/seveas:/git-next/Fedora_23/ # yum -y install git
Fedora 20, 21 and 22 are also supported, just change the download link to match.
To automatically upgrade git, just add a crontab entry that runs the yum or apt-get install command above every day.