When it comes to acoustic guitars, I suggest Yamaha. They make a couple of instruments – the FG800 and FS800 – that are fantastic first guitars. They are affordable, well made and easier to play than most guitars in their price range.
The FG800 has what is called a dreadnought-style body. This gives an instrument excellent projection and a deep, rich sound. It is also the style I recommend for most beginners. The FS800 has a smaller concert-style body. It, too, sounds excellent, but with a little less volume and depth.
Fender makes some good acoustic guitar for beginners as well, and if you are into classical music, you will want to check out Cordoba. Other brands of note include Ibanez, Washburn, Dean and Applause.
As for electric guitars, I recommend two brands for most beginners. The first is Epiphone. This is a company owned by Gibson, and they make a couple of affordable beginner guitars that take after more expensive Gibson models. The Epiphone Les Paul Special II is one, and the SG Special the other.
Both guitars have simple designs that will allow a beginner the opportunity to experiment with different sounds without too much complexity. I usually point newbies toward the Epiphone Les Paul Special II, but either is a smart choice for a beginner.
The other electric guitar brand I recommend for beginners is Squier; specifically the Squier Affinity Stratocaster and Telecaster. Squier is to Fender as Epiphone is to Gibson, and so they make affordable versions of classic Fender guitars. They’re pretty good too, for the price range.
Some other electric guitar brands to check out include Jackson, Ibanez, ESP LTD and Dean.
Remember that this is all based on my own opinions. I encourage you to do your own research and draw your own conclusions.