Tuners often fall into one of a small number of categories – pedal or headstock. That being said, tuning via mobile devices has improved immensely in recent years and can be hard to beat in terms of convenience for those who do most of their playing at home.
Headstock tuners are often desired for their simplicity as much as their scaled down designs - making them perfect for a beginner or someone who has never used a tuner before. They clip on to the headstock of the guitar and interpret intonation through vibration. These tuners were once cheap and cheerful, and never held their own outside of the practice room, but nowadays they can boast some seriously useful tech making them a great option if you don’t use pedals.
Pedal tuners are definitely the most popular choice. With a pedal tuner, you're looking for durability and accuracy. Your tuner will likely find a home among your other pedals and is the pinnacle of set-and-forget, but knowing that it won’t fall apart or give an inaccurate readout is crucial. Place it in the chain in the desired location – usually at the start – and it'll sit there quietly doing its job whenever called upon.
The new kid on the tuning block involves using an app on the phone or iPad you're possibly reading this article on now. While perfect for bedroom practice sessions, this type of tuner is not the one to use if you're out gigging. Getting your phone out mid-set to tune up your guitar isn't the most professional-looking move in the world, and it won't be as accurate as a pedal or clip-on alternative.