The main decision you need to make about a clip-on tuner is this:
1) Will I only ever use this for Guitar? If so, then get this one. The reason I suggest this is that the strings numbers and names will appear on screen e.g. 1E or 2B.
2) Will it also be used for tuning my Violin/Viola/Cello – or maybe even a brother or sister’s? If so, then get this one. Note names will appear on screen, but possibly not string numbers.
For some reason, there is little price difference between the best strings in the world and the worst. So you might as well go for the best. These are the ones I use.