I have a Korg. I like it because it has a "flat" button. Press it once it goes down half a step. Press it twice for a full step. You can go 2 full steps down. It makes tuning in alternate keys easy (Keef Richards uses alternates a lot).

I had one of the better tuners once before, it would recognize all the notes of the scale rather than just E/A/G/D/B/E like most tuners. So if I wanted to tune a string down to "C" or whatever I didn't have to mash any extra buttons.