The arguments for and against pedal, headstock and app tuners continue to rage on, and while some people have very strong views regarding one or the other, all three styles of tuner have a place in the guitar playing world.
Pedal tuners
Pedal tuners are by far the most popular choice when it comes down to it. They're widely regarded as the most accurate type of tuner, as they take a signal directly from your pickups and process it without any airborne interference. A pedal tuner will sit on your pedalboard at the start of your signal chain (after your guitar, of course) and will give you accurate reading after accurate reading – if you've bought a good one, that is.
Clip-on tuners are another popular choice and are famed for their simplicity, portability and versatility regarding tuning acoustic instruments. They're also perfect for someone who's never used a tuner before, as they are hands-on, without too many confusing features. Clip-on tuners are generally the cheapest type of tuner you can get, and a good one doesn't need to set you back more than $25 or $30. There are some proper high-end options available nowadays though, for the headstock tuner enthusiast among us. Especially if you don't use pedals, they're incredibly useful.
Tuning apps are something of a newcomer, although by now they've definitely earned their place. For bedroom or rehearsal room jam sessions, a decent tuner app isn't a bad choice. It's arguably the most convenient option around, as you'll always have your phone on you too. If you're gigging, however, we'd recommend against using an app to tune up. It's not the most professional-looking thing in the world.