Firstly you need to decide whether it is an acoustic guitar or an electric that you want. This is probably the hardest and most important choice you have to make (unless you are rich and can buy both). If you want to learn to play guitar fast, electric may be the way to go, but it's not always easy to transfer what you have learned on the electric to the acoustic, and vise versa. The current trend does seem to be more people buying acoustic from my understanding, but don't let trends decide for you and go for what you want. If you are into rock and heavier music the obvious way to go is electric, if serious about it you can get yourself one from the range of Gibson guitars (as a beginner guitar it's probably best to go for an Epiphone). Or go for a Fender Squier, either of these may cost a little more than the very lowest end of products but they will be much easier to play and sound far better. There's quite a few detailed reviews of some beginner range guitars here http://www.allguitarthings.com
Learning how to play guitar on an acoustic as I mentioned is a bit more difficult, mainly because it's tougher on your fingers which is a common problem for new players. A bonus is there are more cheap guitars of this type (although the quality at the very lowest end is pretty shocking). If you are into more folk music or just want to play a few guitar chords and have a sing-a-long, the acoustic is probably your safest best. (don't worry if you aren't as good as this little guy, what an insane talent he has!). I recommend going for one with steel strings too unless you are particularly fond of artists that play with nylon and you have a preference for that sound, steel strings will also mean transitioning to the electric would be an easier task if that's what you wanted to do in future. http://en.wikipedia.org/wiki/Acoustic_guitar check this to read all the different types of strings, there's a list mid way down the page.
Then there's always the best of both worlds option - the electro-acoustic, these can be very good and indeed if you have desires to be performing in more than just your bedroom, this is a good option. You of course lose most of the acoustic sound when you plug in though, as the hollow body does nothing, it's all about the pickups. (Yet another alternative would be to buy a better acoustic guitar then later down the line install your own pickups into it/get an expert to do it - it's quite easy).
Thanks for reading and remember ultimately it's not the end of the world if you make the wrong choice, in many cases you will be able to return to the vendor and if not you could sell it on second hand online and get most of your money back and then buy a guitar. Or do what I did and battle on through, with enough practice you can make anything work!
