A distribution is a collection of programs that will make up of what you will be installing in your PC besides the Linux kernel. A distribution is like an accent. A lot of people are saying the same thing but they are just saying it differently. Some more so than others. More importantly, choosing a distribution is like choosing a path. It will lead you to same place, just a different entrance into the city. Also the road can be winding but dotted with friendly towns or it can be 5 lanes wide chock-ful of people, leading the directly to the location. Ok, enough with the anologies.
Choosing a distribution over another will affect you in the following way:
- How regular the software is updated. Which may translate into how long will you be exposed to a known venerability after it's made known. A more active distribution will have updates and patches available as soon as possibe. Most of them do because the nature of a distribution is that it is created by people and used by them. More likely, it'll translate into how long before you will be able to use that latest program or software you heard about.
- Selection of pre-packaged software. Some distributions are general purpose, others are catered for a specific group of people. There are also distributions that you don't have to install. They run directly from CDs or DVDs. In this case, your choice is about use rather than having it sit on your hard disk. You might choose to use something off the CD for a while until you decide it is worthy to sit on your hard disk.
- How long will it be supported after the version number rolls over. This is usually short, may be about a year or so for most non-commercial distributions. There is a reason sometimes some new features can't be included in the older version of the distribution.