If you are going to play a guitar the first thing you need to do is learn to tune it. In the old days you needed a reference tone from a piano or maybe even a pitch pipe. Using a reference tone required you to match the tone of your guitar to the reference tone, using your ear, to get the tuning right. Thank your luck stars technology has smiled on guitar tuners everywhere and there are now a multitude of tuners available and you don't even have to hear the sound your guitar is making to get the tuning right. 

Believe it or not, I used to use a Banana to tune my guitar. No, not the yellow kind silly. My Banana was a little electronic box with a little meter and needle. It had a microphone to pick up the sound from an acoustic guitar and a jack to plug in an electric. The Banana listened while you played a string and the little needle would move. If the needle was left of the center of the meter you tightened the string and if it wnet to the right of center you loosened the string. When the needle stayed in the center you were in tune. While the Banana worked reasonably well, and was a vast improvement over a reference tone, modern tuners are even easier to use. You can even find one that will turn the pegs for you and bring your guitar into tune.

I still have my old Banana somewhere but have found something I think is even better for accurate guitar tuning. I suggest getting a tuner that uses lights to indicate whether you are in tune. My little Sabine tuner uses two rows of lights to indicate the proper tuning. The top row includes red lights to the left and right and a green light in the middle. Get the green light to stay lit and you have the proper tone. The bottom row of red lights gives sharps, flats and naturals for every note in the scale. If you want to vary your tuning from standard this light arrangement is an excellent solution. The Sabine can tune an acoustic or electric. It has a built in microphone, input and output jacks to accomodate your tuning needs. Sabine also makes a version of the tuner that mounts to the guitar so no more balancing the tuner on your knee.

I also have  a stage tuner that works on the same principle as my Sabine. The only difference is it sits on the floor and your guitar cord goes in one side and a cable to your comes out the other side. You activate the tuner (and take your guitar offline) by stepping on the tuner button. I great tool for gigs.

I mention the Sabine line of tuners only because that is what I use. There are many other brands and types of tuners available and you may find one you like better than a Sabine but that is for you to decide.

Regardless of what I say here or what other reviewers or players may tell you, the best tuner for you is going to be the one that you find works the best and is the easiest for you to use.