There are three main types of guitar tuner. Once you peel back the marketing hype, the main difference comes down to personal preference:
Chromatic: The first is chromatic. These tuners compare the input signal to one of the 12 notes in the chromatic scale. This means they are limited to only these notes, as well as only tuning one note at a time. For most players, neither of those limitations is likely to be an issue.
Polyphonic: The second type of tuner is polyphonic. Just as with pitch-shifters or synths, 'polyphonic' simply means that the tuner can process multiple notes at once. The downside, of course, is that this is harder to show to the user. They can be incredibly useful live, however, as you can strike all the strings to see if everything lights up green.
Strobe: The final type of tuner is the strobe tuner. Unlike the chromatic tuner, the strobe tuner can be set to custom frequencies and temperaments. This is very useful for players that play music outside of standard Western scales. It can also be useful for experimenting with different pitch standards, like basing around 432Hz instead of 440Hz. Though this sounds esoteric, Soundgarden's smash Black Hole Sun used 432Hz and many artists favor the standard. Strobe tuners are typically the most expensive and specialist of the three.
Generally speaking, although it's a matter of taste, you can't go wrong with a chromatic tuner as long as you're working within standard Western scales.