I'm often asked by aspiring guitarists (or for young guitarists, their parents) which is the best guitar for a beginner.
The best advice is what I heard from my guitar teacher: get the one you want to play. A guitar that you find fun to play will make you want to practice, and practicing will make you better and want to play more. A guitar that suits the music you love may give you more joy than one that is designed for other genres.
Nonetheless, I would like to share some principles that may help in choosing your first guitar.
Easy to Play
One of the pains of initiation as a guitar player is to develop callouses on your fretboard hand. This takes weeks and hours of uncomfortable practice. You can spare yourself some of the pain by starting with a nylon string or electric guitar, as a steel string acoustic guitar is roughest on the fingers. A 12-string guitar is even tougher to learn on; I would steer clear unless you have a powerful attraction to Tom Petty and George Harrison songs that demand 12-string.
The Right Size and Weight
Another usability factor is the size of the guitar, and for electric guitars, the weight.
Acoustic guitars come in several sizes, from parlor to dreadnought. Try them out and see how comfortable they feel sitting and standing. I prefer a small bodied acoustic with a wider neck, for instance.
The size problem is particularly acute for children. Smaller 1/2 and 3/4 size guitars are available for children. Some will not support standard tuning so be sure to check for this when purchasing.
How Much to Spend
Entry level guitars are surprisingly inexpensive, and the cost of quite serviceable instruments has decreased over the years even as quality standards have improved.
Nonetheless, there are inexpensive guitars that can justifiably be called cheap because their quality is not good enough to serve a player. They can create frustration if they are uncomfortable to play, do not stay in tune or has poor intonation (notes that are true throughout the neck). Some problems can be solved by a setup by a guitar technician.
I have two friends who bought electric guitars that turned out to be duds. One was a non-name solid-body guitar on eBay and one was a Fender Squier Stratocaster. Both of them were disappointed with the guitars which they ended up abandoning for more reliable instruments.
There is a healthy market for used guitars, and you can take advantage of it for starter guitars. You could also purchase a nicer used guitar (say $500) and sell it later for nearly what you paid for it.
Where to Buy
I recommend that you purchase your first guitar at your favorite local music store. People who work at the store are knowledgeable and will stand behind their instruments. When you have questions, the music store will be able to help you, and they often host music teachers or can connect you to a guitar teacher.
Since I live in Washington, DC, I am fortunate to have several great music stores. The best one for guitars is Washington Music Center (also known as Chuck Levin's). Going to Chuck's is a great experience, like a bazaar for musicians with tremendous selection of all the top brands and sales staff that are top notch. It will remind you of the music store in Blues Brothers. In my neighborhood we have Middle C Music which offers instruments, excellent music classes and a wide selection of sheet music and books for all instruments. As you might expect, Guitar Center offers a wide selection.