LTS are usually for business, and are usually more stable, and the server version is supported for 5 years.
https://wiki.ubuntu.com/LTS has some pretty pictures.
Cons of upgrading each release
Upgrading each release is
- A pain
- a small risk; new release may contain bugs that the previous one didn't, or may be less stable
Pros of upgrading each release
- You get newer versions of programs though apt-get (Although that is not a problem if you install from source)
Upgrading vs Clean install
I will always prefer clean installs, but this is a personal preference, and doesn't really have a solid grounding. However saying that every time I have upgraded there always seems to be some small annoying problem that a clean install gets rid of.
I suppose a clean install will also allow you to think about what programs are actually needed, and allows you to have a clean start, installing root kit checkers, etc
I will always use LTS releases for my servers. If I want the absolute latest program I will install from source, but then bear in mind that you will have to update these manually.
LTS may not get the latest and greatest, but will be pretty solid and stable, and will get security updates.
As you would like to benefit of the major version upgrades of MySQL / Apache / PHP I would install these from source.
But again this is all personal preference based on nothing more than a couple of years experience
How do enterprises usually do?
I would assume they all use LTS as that is who it is designed for!
If you do decide to upgrade each release, I would have a 'test' server that I would upgrade first, run for at least a couple of weeks to make sure there are no problems, before upgrading the whole lot.