Left-handed guitarists have to make a choice between whether they want to play a regular right-handed guitar or a left-handed guitar. There is no simple answer to this question and unlike issues such as left-handed scissors there are legitimate questions as to whether a left-handed guitar is easier for a left-handed player.
First it is necessary to examine why a standard right-handed guitar is held in the direction of the neck pointing to the left. This tradition of the guitar being held to the left like many of the traditions in guitar comes from the classical guitar which was the dominant guitar style when the guitar was being developed. Until the 20th century the guitar, both classical and popular, was mostly played by finger-picking instead of with a pick. In finger-style guitar both hands are performing complex and difficult tasks but the finger-picking right hand is the one performing the more complicated tasks. For this reason the right-hand was given the finger-picking task and the left-hand the fretting task resulting in the guitar pointing in the leftward direction.
In the last century, playing the guitar with a pick has become much more popular and widespread to the point where there are far more players who can play with a pick than with their fingers. Picking with a pick is a much simpler procedure than finger-picking yet the direction of the guitar has remained true to tradition. I would argue that theoretically for right-handed guitarists who have no intention of finger-picking, it may actually make more sense to play a left-handed guitar since the stronger right hand would be the one doing the fretting which is more complex than picking with the pick. Thus, I don't think that left-handed guitarists playing with a pick are at any disadvantage playing a right-handed guitar and may actually be at an advantage.
For guitarists who want to finger-pick or who think they may want to do so in the future, the issue is more complex. While the finger-picking hand is generally considered the more complex and difficult of the two hands, both hands are performing complicated and difficult tasks. Any advantage won by switching one task to the strong hand has its counterpart in that the task performed in the other hand suffers an equal disadvantage. The question is whether the advantage of having the strong hand for the finger-picking hand outweighs the disadvantages of playing a left-handed guitar. It should also be noted that there are many left-handed finger-pickers who still pick very well even though they are finger-picking with the right-hand.
The disadvantages of playing a left-handed guitar is that these guitars are much harder to get and usually more expensive than their right-handed counterparts. Many companies do not even make left-handed instruments and those that do often only produce a limited number of their models in left-handed versions. If you play left-handed you have to accept that you may not be able to buy the exact guitar you want and even if you are able to buy it you will probably have to pay more for it. While this may seem unfair it does cost guitar manufacturers a significant amount of money to change their machinery to produce left-handed guitars. Considering that approximately 10% of the population is left-handed and that of those left-handed guitar players probably more than 50% play right-handed guitars the market for these guitars is limited. Additionally one has to consider that guitar is one of the few instruments in which a left-handed version is available. For example, although there are examples of left-handed pianos they are extremely rare despite the fact that a left-handed pianist is probably at more disadvantage playing a right-handed instrument than a left-handed guitarist.
The major disadvantage to playing a left-handed guitar is not the lack of instrument selection and cost but the fact that you will not be able to play a standard guitar. Every time you are at a party and someone hands you a guitar you will not be able to play it. If you want to play guitar you will almost always have to have your own guitar around while if you played a right-handed guitar you would be able to borrow other people's guitars or use whatever guitar is lying around. Students that I have had who have played left-handed guitars have told me that this is incredibly frustrating.
I am not left-handed myself and am not advocating that all left-handed players play right-handed guitars. I do, however, think that left-handed beginning guitarists need to give some serious consideration to whether there is any advantage to playing a left-handed guitar and whether this advantage outweighs all of the disadvantages. Above all one should not assume that because you are left-handed and there is a guitar that is called left-handed it is necessarily better for you in the way that a left-handed pair of scissors would be. I would recommend that any left-handed person who is buying their first guitar try out both left and right-handed guitars to find out which feels more comfortable. If the left-handed version feels much better for you then it is probably better to play a left-handed guitar. If you find there is no significant difference then it is probably better to choose a right-handed guitar.