Two types of strings: Steel and Nylon

There are two main string materials: steel and nylon. You will find steel strings on acoustic guitars,

...and electric guitars: 

You will find nylon strings on classical guitars:

Which do you like the sound of, best?

Choosing a sound or tone that you want is a great way to figure out which type of string, and what type of guitar, is best for you. Steel strings tend to have a sharper tone, while nylon strings are more mellow and rounded.

If you want to play electric guitar, you don't have much choice: you'll have to go with steel strings. But, if you are looking to play acoustic guitar, you'll have the option of choosing between nylon or steel strings. 

Here's a fingerpicking example as played on a steel string and a nylon string guitar, starting with a steel string acoustic guitar.

Here's a strumming example as played on a steel string and a nylon string guitar, again, starting with a steel string acoustic guitar.

Notice the differences and ask yourself which one you like best. This can really help you make a decision about the best kind of guitar for you.

Steel strings are rough at first, but are better later on

I might as well give you my opinion about which is best type of guitar to start to start learning on: Steel string acoustic guitar. Why?

Callouses can form faster with steel strings than they can with nylon. It's also generally agreed upon that if you start with acoustic steel stringed guitars it's easier to switch to electric guitar later on.

Photo Cred: lost inspiration? by robb p, Attribution 2.0 Generic