The type of guitar to buy generally depends on the style of music you want to play. Other considerations include age, size, ability and budget.
A rough guide for guitar sizes:
3/4 size for children aged between 6 and 11.
Full size for children over 11 and adults.
Classical guitars have nylon strings which are easier to hold down than the strings on steel string acoustic guitars. If you buy an electric guitar you will also need to buy a guitar amplifier. For these reasons many students begin learning on a classical guitar and then change to a steel string acoustic or electric guitar if they want to learn these styles later on. Some students start straight away on electric or steel string acoustic guitars and get on fine. The majority of students I teach at primary school have 3/4 size classical guitars.
Students who are ready and who want to take grade exams will need to have the right type of guitar for the style of music and syllabus they have decided to follow.
There is a wide variety of instrumental solo music for the classical and spanish guitar so you don't need to be able to sing or be in a band if you choose this style.
Steel string acoustic guitars are great for acoustic rock, folk, blues and many other genres.
Electric guitars are best for students interested in playing rock, pop, blues, jazz etc ... and for those aspiring to be in a band.
The bass guitar is used for a wide range of genres. There seems to be fewer bass guitarists than electric guitar players. If your ambition is to join a band you will probably be in demand as soon as you can play!
I would strongly recommend buying a guitar from a specialist music shop which can let you try out different guitars before you buy, set the guitar up properly and provide a good after sales service.
Guitar Bag / Guitar Case