Trying to make sense out of choosing a Linux distribution is an art, or is it a science. I guess that too depends on what kind of person you are. Most likely you are looking for a desktop Linux to supplement (dual-boot with MS Windows) or to replace MS Windows altogether. Selecting a desktop version of Linux narrows down the field quite a bit. This eliminates the server editions and a lot of the special focus versions out there. I really wish there was a spreadsheet or database listing all the options in one place. Wikipedia has a chart under "Comparison of Linux Distributions" but I think it needs some refinement so that new folk can quickly grasp an over all view. With all Linux distros there are some elements that are alike and some that are standout and value added features. The whole idea is to pick one distro as a base and then add or delete stuff until it suits your needs. If you are a picky user, this can get quite involved. I am going to give you the big choices and point out some of the small ones you are likely to encounter.
1. Distro name - name recognition is strong indicator of what's behind it. Like Red Hat, Suse, Ubuntu. Would you like a company, a small group or a couple of people behind your distro. In any case you have to investigate and consider. If not, then look at what's popular and consider it a start, you are free to change your mind. Consider support and updates.
2. The desktop - KDE, Gnome, Xfce, Fluxbox, or whatever is right for you. You can go fat or lean, full featured or minimum. In theory, you can put your desktop preference on any distro you choose.
3. The package management system - RPM, Debian, Targz, or CNR. There are also programs that will convert one format into another. The question to ask is if this distro with this format has the software you need in its repository's, are they current, and can I install/delete them without a lot of hassle.
These to me are the biggies. Then there are small but important stuff that hit and run users don't usually haggle over, like administration tools and utilities that you tweak the system and desktop with.
Don't neglect to look at these as this is where the value added features come to play. Often these features define and make or break a distro. But, in theory, it doesn't matter which distro you start off with. You should be able to find the same stuff that is in other distros to put into your distro. I am saying there is only one Linux, it has many, many parts to choose from and that a distro is some pre-selected parts already grouped together for you.
If you are a wet finger in the wind kind of weatherperson, there are some web sites that have "distro chooser" programs. My favorites are www.linux.org/dist/ and www.polishlinux.org. You just answer the questions and they put you in the ballpark. Then with your choices in hand go to www.distrowatch.com or to www.livecdlinux.com to find info or download sites.
Do I have any recommendations? Yes and I have opinions too.
The full featured major distros are fine but I think it is fun to consider the smaller ones too. Ask yourself if it's easier to add or delete stuff. With the live-CD Linux you can try before you install, no harm done if you don't like it. If you like a particular desktop, that desktop will make different distros look and feel the same. In that case it's the added value features that matter. My choices are full featured but a little leaner desktop Xubuntu and for a smaller distro I like Wolvix. I like DreamLinux and Puppy also. There is nothing good or bad about other distros, taste, choice, fit, are all subjective things. If you are into performance or resource use or laptops, you can look into those things as well on user forums. Relax folks, Linux is fun and you can afford to be picky, it's OK because there is no one size that fits all.