The electric guitar is better for playing rock guitar and getting a hard or heavy rock sound. The acoustic is generally not used used as the main guitar in rock is generally used for ballads or quieter songs.
First you want the right type of guitar. The best well known brands, particularly for Classic Rock guitar music, are the Fender Stratocaster and the Gibson Les Paul.
Epiphone is the value version of Gibson and Fender also has a value version in the Fender Squier brand. There are more modern guitar brands like Jackson Guitars, ESP, B.C Rich, Yamaha or Ibanez.
Try and get a guitar with a Humbucker pickup. Looks like a double pickup, see the pickups on the Gibson Les Paul guitar above. This will give you a fat meaty rock sound. Get a guitar with at least two pickups on it as well. Three pickups are nice but not totally necessary. One pickup will limit your sound.
One guitar to avoid which is not associated with rock is the Fender Telecaster, it has a bigger association with country music.
Guitarists often use lighter gauge strings, 9′s to make it easier to play, string bend etc. Lighter gauges also give a lighter sweeter tone. Heavier gauge strings, 12′s can give a richer more solid heavy sound though. The string gauge is up to individual taste. As you learn to play rock guitar, you probably should start off with a lighter gauge for ease of guitar playing and then go up to 10′s, then 12′s or whichever gauge you choose, as you become better.
The Guitar can also have a tremolo bar which used during lead solos. The Floyd Rose tremolo is the best for keeping strings in tune. The bridge floats when not used. You won’t need a tremolo when you begin guitar lessons so it is not necessary at the very start.
The next piece in your sound is the guitar amplifier. The amp amplifies the sound from the electric guitar. Best known brand is of course the Marshall amp, which of course comes in a stack. There are loads of other good brands such as Vox, Fender, Gibson, Roland, Peavey and Laney.
A 15 watt amp is good enough to begin with as a practise amp. You can get a lot of noise out of 15 watts. You can get bigger ones, 25 watts etc, when or if you plan to play in public. Some amps come with built in effects such as distortion or more probably an overdrive switch which are handy for playing rock guitar. Only thing is the effect are hard to switch off when you are playing. You need to stop your guitar playing for a moment to hit the switch which interrupts the guitar music.
An amp is essential, doesn’t matter if you have a built in effect or not on it. You should try and practise your guitar lessons on the amp as you learn to play guitar. When you play the guitar amplified you get a different sound. You also get unwanted sounds amplified such as the noise of your fingers sliding or fingers and pick hitting the strings wrong (pick attack sounds) or buzzing of untouched strings. Practising with the amp will teach your to damp these unwanted sounds.
You can also buy a noise gate to cut off these unwanted sounds. But you need to set it under a certain level or else you also cut off your wanted guitar notes as well as your unwanted sounds.
In the next part we will take a more in depth look at Guitar effects.