Guitar tuners are split into three main types. Many companies will claim that different tuner types enable greater accuracy or easier usability, but really it all comes down to personal preference.
Chromatic tuners are probably the most common type of tuner. These tuners collect your input signal and compare it to one of the 12 notes in the chromatic scale. They'll then find the note it's closest to, and guide you up or down to match the pitch. Chromatic tuners are, by nature, limited to only those 12 notes (in a number of octaves nonetheless) but if you're working within the common 'Western' scales, this shouldn't be a problem.
Polyphonic tuners are also quite common, and their popularity is rising with the likes of the TC Electronic PolyTune series. Polyphonic tuners are equipped with the capability to process multiple notes at the same time, which can make tuning much quicker. The downside to polyphonic tuning is that it's harder to show the user exactly which strings are out of tune – especially if they're mid-set or using a pedal tuner.
Strobe tuners are less popular than the other types of tuners, but what they lack in popularity, they make up for in usability. Strobe tuners can be set to custom frequencies and temperaments, making exploring new tunings much easier – and for those who play music which is outside of the common 'Western' scales, strobe tuners are almost a necessity. If you're interested in using 432Hz as your base instead of the usual 440Hz, then a strobe tuner could be just what you need. They're a bit tough to decipher at first, but once you get the hang of them, they're very useful pieces of gear.
If you've got no overriding preference after reading that, then a chromatic tuner will likely see you right. They're the most popular option for a reason, after all.