One rule to choosing the right guitar tuner
There are many guitar tuners out there, but the better ones have one specific feature that comes in very handy.
Above is a Korg GA-50. Very simple with a nice large display, very easy to operate and tunes by built-in microphone (for acoustic guitars) or direct input (for electric guitars). Notice that it can output sound itself for tuning by ear, and it has an output jack on the left. It even has a little pop-out stand on the back so you can prop it up when placed on a desk.
The GA50 is one of the best designed guitar tuners there is, no question about it.
There is however one thing about it that I really, really like. The dedicated "FLAT" button.
I mainly play in Eb these days, and the fact the GA-50 has a FLAT button is oh-so nice. It's right there, right in front. Just push a button and you got it.
Clip-on tuners can all tune flat, obviously. But there are two issues. First, the button to make it flat is almost always in the back. Second, the indicator for flat - if the tuner even has one - is tiny and almost unreadable, requiring you to crane you neck towards the headstock of your guitar just to see it.
On the GA-50, you get a button. An obvious button. On the front. And you know when the tuner is set to flat tuning.
The GA-50 may be a cheap little tuner, but it's the thoughtful design of it that really makes it awesome.
Oh, and one last thing to know about this tuner - when playing at home, you usually don't even have to plug your electric guitar in to tune with this. Just set your amp to clean at a lower volume, use the microphone on the GA-50 to listen for notes, and it tunes just as good as when using direct input... which actually makes it easier than using a clip-on tuner.